Hydrocarbon conversion process utilizing a magnetic field in a fluidized bed of catalitic particles

ABSTRACT

A hydrocarbon conversion process, such as catalytic desulfurization of a vaporized petroleum feedstock with hydrogen or catalytic reforming of a vaporized hydrocarbon feedstock, is carried out by passing the gaseous medium upwardly through a fluidized bed of magnetizable composite particles having catalytic activity for hydrocarbon conversion and which contain 2 to 40 volume % ferro- or ferrimagnetic material to a nontime varying (direct current) and substantially uniform applied magnetic field having a substantial component along the direction of gravity such that the composite particles have a component of magnetization along the direction of gravity. The gaseous medium is also the fluidizing medium passing upwardly at a superficial gas velocity ranging between: 
     (1) at least twice the normal minimum superficial gas velocity required to fluidize the bed in the absence of said applied magnetic field, and 
     (2) less than the superficial gas velocity required to cause time-varying fluctuations of pressure difference through said bed for a 0.1 to 1 second time interval during continuous fluidization in the presence of said applied magnetic field.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 786,613, filedApr. 11, 1977, now U.S. Patent No. 4,115,927, granted Sept. 26, 1978,which in turn is a continuation-in-part of application Ser. No. 610,071,filed Sept. 3, 1975, and now abandoned, which in turn is acontinuation-in-part of application Ser. No. 514,003, filed Oct. 11,1974, now abandoned.

FIELD OF THE INVENTION

This invention relates to a fluidized bed process. More particularly,the present invention is concerned with a process for operating amagnetically stabilized fluidized bed under conditions such that theflow of gas used to fluidize solid particulate magnetizable andfluidizable particles and an applied magnetic field are controlled tothe extent that there is substantially no time-varying fluctuation ofpressure at a point taken in the bed. Such a magnetically stabilizedmedium has the appearance of an expanded fixed bed; there is no grosssolids circulation and very little or no gas bypassing. A bed of themagnetically stabilized medium shares many qualities of the normalfluidized bed; pressure drop is effectively equal to the weight of thebed divided by its cross sectional area, and independent of gas flowrate or of particle size; the medium will flow, permitting continuoussolids throughput. Beds of the magnetically stabilized media also sharesome of the qualities of a fixed bed; countercurrent contacting can bereadily attained; gas bypassing is small or absent, making it possibleto achieve high conversions and attrition is minimal or absent.

The simultaneous possession of properties usually associated with themedia of fixed and of fluid beds is highlighted, for example, in the useof a magnetically stabilized medium to trap particulates. Like themedium of a fixed bed, it will trap the particulates; like the medium ofa fluid bed, it will not clog -- the pressure drop of a bed of themedium will increase only by as much as due to the weight of the trappedmaterial.

BACKGROUND OF THE INVENTION

Many chemical and physical processes such as catalytic cracking,hydrogenation, oxidation, reduction, drying, polymerization, coating,filtering and the like are carried out in fluidized beds. A fluidizedbed briefly, consists of a mass of solid particulate fluidizablematerial in which the individual particles are neutrally levitated freeof each other by fluid drag forces whereby the mass or fluidized bedpossesses the characteristics of a liquid. Like a liquid, it will flowor pour freely, there is a hydrostatic head pressure, it seeks aconstant level, it will permit the immersion of objects and will supportrelatively buoyant objects, and in many other properties it acts like aliquid. A fluidized bed is conventionally produced by effecting a flowof a fluid, usually gas, through a porous or perforated plate ormembrane underlying the particulate mass, at a sufficient rate tosupport the individual particles against the force of gravity.Conditions at the minimum fluid flow required to produce the fluid-like,or fluidized condition, i.e., the incipient fluidization point aredependent on many parameters including particle size, particle density,etc. Any increase in the fluid flow beyond the incipient fluidizationpoint causes an expansion of the fluidized bed to accommodate theincreased fluid flow until the gas velocity exceeds the free fallingvelocity of the particles which are then carried out of the apparatus, acondition otherwise known as entrainment.

Fluidized beds possess many desirable attributes, for example, intemperature control, heat transfer, catalytic reactions, and variouschemical and physical reactions such as oxidation, reduction, drying,polymerization, coating, diffusion, filtering and the like.

Among the problems associated with fluidized beds, a most basic one isthat of bubble formation, frequently resulting in slugging, channeling,spouting, attrition and pneumatic transport. This problem is most commonin gas-fluidized systems. Bubbling causes both chemical and mechanicaldifficulties: for example, in gas-solids reaction gas bubbles may bypassthe particles altogether resulting in lowered contacting efficiencywhile chaotic motion of the bed solids may set up detrimental mechanicalstresses tending to deteriorate the vessel and its contents. Manyprocedures and systems have been proposed to effect improvements, forexample, by the use of baffles, gas distribution perforated plates,mechanical vibration and mixing devices, the use of mixed particlesizes, gas plus liquid flow schemes, special flow control valves, etc.

for example, U.S. Pat. No. 3,169,835 to Huntley et al disclose that meshpacking throughout the bed breaks up large gaseous bubbles and preventscoalescence of existing bubbles. However, baffle devices do not preventthe initiation of bubble formation.

DESCRIPTION OF THE PRIOR ART

In recent years patents have issued which describe means for suppressingbubble formation in a fluidized bed. For example, U.S. Pat. No.3,304,249 to Katz discloses that a stabilized fluidized bed is obtainedwhen a bed containing solids having a moderate surfaceelectroconductivity is fluidized by a gaseous medium having asufficiently high ionizapotential to provide a corona discharge withoutarcing and subjecting a high voltage to a portion of the bed to cause acorona discharge in the fluidized bed.

In another patent, U.S. Pat. No. 3,439,899 to Hershler, there isdislosed a process for producing a fluidized bed free of bubbles bypassing a fluid upwardly through a particulate solid fluidizablematerial which includes a plurality of discrete magnet particles havinga coercive force exceeding 50 oersteds to impart an upward force to thesolid particulate fluidizable material and subjecting the fluidizablematerial to a magnetic field varying with time in direction andintensity to impart individual motions to the magnet particles. Asimilar process is disclosed in U.S. Pat. No. 3,219,318 to Hershler. Z.I. Nekrasov and V. V. Chekin, in their articles appearing in Izv. AkadNauk. USSR, Otdel, Tekh, Nauk, Metallurgiya i Toplivo at 6, 25-29 (1961)and at 1, 56-59 (1962) disclose that the formation of bubbles and slugsin a fluidized bed may be eliminated over a wide range of variation offlow rates by a laterally applied variable magnetic field due to theinteraction of this field with fluidized ferromagnetic particles.

U.S. Pat. No. 3,440,731 to Tuthill discloses a process for stabilizingand suppressing bubble formation in a fluidized bed, containingparticulate solids having ferromagnetic properties by subjecting thefluidized bed to a magnetic field. While it is disclosed that either analternating current or a direct current electromagnet may be used, theonly example in the patent describes an alternating currentelectromagnet, thus producing a magnetic field varying with time indirection and intensity.

Numerous publications by Ivanov and coworkers and a publication bySonoliker et al disclose the application of a magnetic field producedfrom a direct current (nontime varying) electromagnet to fluidize ironor iron-chromium particles such as used in ammonia synthesis or carbonmonoxide conversion. These articles include: Sonoliker et al, IndianJournal of Technology, 10, 377-379 (1972); Ivanov et al ZhurnalPrikladnoi Khimii, 43, 2200-2204 (1970); Ivanov et al, ZhurnalPrikladnoi Khimii, 45, 248-252 (1972); Ivanov et al, InternationalChemical Engineering, 15, 557-560 (1975) (also published in ChemicalIndustry, 11, 856-858 (1975)) and The Soviet Chemical Industry, 6,713-715 (1974); Ivanov et al, Comptes rendus de l'Academie bulgare desScience, Tome 25, No. 8, 1053-1056 (1972); and Ivanov et al Comptesrendus de l'Academie bulgare des Science, Tome 23, No. 7, 787-790(1970). In some of the published work of Ivanov and coworkers a gradientapplied magnetic field is used to generate body forces to hold fineparticles in place and thus permit higher flow rates than inconventional beds. For example, the work reported in British Pat. No.1,148,513 and Ivanov et al., Kinet. Katel; 11, No. 5, 1214-19 (1970)varied the direction of the field from transverse to axial in relationthe flow.

In general, the published works of Sonoliker et al and Ivanov et al,teach that higher gas velocities can be used in the presence of anapplied magnetic field than in its absence. For example, Ivanov et al.state in Zhurnal Pikkladnoi Khimii, 45, 248-252 (1972) at page 251:"Linear gas velocities higher by 30-40% can be used under high pressurein the presence of a magnetic field than in its absence, at the samedegree of bed expansion without appreciable breakdown of the bedstructure and without transport of particles out of the bed." However,Sonoliker et al and Ivanov et al provide no recognition of the existenceof the stably fluidized non-bubbling bed and appear to erroneouslyinterpret the transition from the stably fluidized state to the unstablyfluidized (bubbling) state as the transition from fixed to fluidizedstates. Furthermore, they did not teach the essential role played byorientation and the significance of role played by uniformity of theapplied magnetic field. In a uniform applied magnetic field, the bed isfree of any net magnetic force.

Workers at the Brookhaven Laboratories, H. Katz and J. T. Sears, Can. J.Chem. Eng. 47, 50-53 (1969) described a process for the stabilization ofa fluidized bed of dielectric particles by use of an electric field.These workers disclose that glass bead and silica gel particle beds wereobserved to behave as packed beds at flow rates (and pressure drops) offluidizing gas up to 15 times the normal incipient fluidization rate.Katz and Sears also disclose in the cited article the use of an imposedaxial magnetic field (alternating or unidirectional) to stabilize a bedof iron particles, but indicate that the iron particles under theinfluence of a strong magnetic field are in the form of a slug.

THE DISCOVERY OF THE PRESENT INVENTION

It has been discovered that by fluidizing a bed containing solidparticulate magnetizable and fluidizable material with a fluid such as agas or liquid in the presence of an applied uniform, time-steadymagnetic field oriented parallel with the direction of fluid flow, astably fluidized bed results over a substantial range of gas velocities.

The basis for the phenomenon is believed to relate to the behavior ofmagnetic stress in the fluidized medium which is viewed as a homogeneousmagnetized continuum. A local perturbation in voidage modifies theuniform magnetic stress of the unperturbed bed creating magnetic forcesthat tend to restore the medium to the uniform state. A generalexpression for the magnetic stress tensor is provided inFerrohydrodynamics, Entry in the "Encyclopaedic Dictionary of Physics,"Suppl. Vol. 4, by R. E. Rosensweig, Edited by J. Thewlis, Pergamon Press(1971).

SUMMARY OF THE INVENTION

As one embodiment of the present invention there is disclosed a processfor fluidizing a bed containing solid particulate magnetizable,fluidizable material and fluidizing fluid located within an externalforce field wherein at least a portion of said bed containing said solidparticulate magnetizable, fluidizable material and fluidizing fluid aresubjected to a nontime varying and substantially uniform appliedmagnetic field having a substantial component along the direction of theexternal force field such that said solid particulate magnetizable,fluidizable material has a component of magnetization along thedirection of the external force field and wherein at least a portion ofsaid bed containing the solid particulate magntizable, fluidizablematerial is stably fluidized by the flow of fluidizing fluid opposingsaid external force field at a superficial fluid velocity rangingbetween:

(a) more than the normal fluidization superficial fluid velocityrequired to fluidize said bed in the absence of said applied magneticfield; and,

(b) less than the superficial gas velocity required to causetime-varying fluctuations of pressure difference through said stablyfluidized bed portion over a finite time period during continuousfluidization in the presence of said applied magnetic field. The normalminimum fluidization superficial fluid velocity is the fluid velocityobserved when the pressure difference of the fluid passing through thefluidized bed, as measured between the upper and lower surfaces of thebed, is first substantially the same as the bed weight per unitcross-sectional area.

The strength of the magnetic field and its minimal deviation from acolinear orientation to the external force field are maintained so as toprevent and/or suppress formation of bubbles in the fluidized media at agiven fluid flow rate and with a selected fluidized particles makeup.

Fluid throughput rates which are up to 10 to 20 or more times the flowrate of the fluidized bed at incipient fluidization in the absence ofthe applied magnetic field are achieved, concomitant with thesubstantial absence of bubbles. The magnetically stabilized fluidizedbed has the appearance of an expanded fixed bed with no gross solidscirculation and very little or no gas bypassing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation comparing the magneticallystabilized fluidized bed of the present invention with an ordinaryunstabilized fluidized bed.

FIG. 2 is a graphical illustration of a three phase diagram displaying(1) the solid unfluidized region, (2) the stabilized, fluidized region(the operating region or zone of the present invention) and (3) thebubbling fluidized region, as a function of applied magnetic fieldintensity and stabilizing velocity.

FIG. 3 graphically illustrates the expansion of the magneticallystabilized fluidized bed in response to increasing gas flow at aconstant applied magnetic field intensity.

FIG. 4 graphically illustrates the three phase regions, i.e., (1) thesolid, unfluidized region, (2) the stabilized fluidized region and (3)the bubbling fluidized region as a function of applied magnetic fieldintensity. The experimental system in this Figure is the same as used inFIG. 3. The bed depths in this experimental system may be read from FIG.3.

FIG. 5 graphically represents the pressure drop of 177-250 micron steel(C1018) spheres as a function of superficial gas velocity at a uniformapplied magnetic field of 48 oersteds.

FIG. 6 graphically represents a three phase diagram resulting from theplotting of the minimum fluidization velocity and the transitionfluidization velocity as a function of an applied uniform magneticfield. The experimental system is the same as used in FIG. 5.

FIG. 7 illustrates a correlation of transition modulus N_(m) withtransition velocity voidage ε_(o) which supports the conclusion ofdimensional reasoning that a unique relationship exists between thesetwo variables for magnetically saturated, long beds. The supportednickel material has a density of 1.30 g/cm³ and a magnetization of 5000oersteds at an applied field of 228 gauss.

DETAILED DESCRIPTION OF THE INVENTION

As indicated previously, the present invention relates to a process foroperating a stably fluidized bed over a substantial range of fluidvelocities. Fluid throughput rates which are 2, 5, 10, 15 and 20 or moretimes the normal minimum fluidization superficial fluid velocity of thebed containing the fluidizable material can be accomplished by thepractice of the invention concommitant with substantial absence of grosssolids circulation, very little or no gas bypassing and minimal orabsence of bed fluctuation. The fluidized bed is stabilized bysubjecting at least a portion of the fluidized bed comprising solidparticulate magnetizable and fluidizable material and a fluidizing fluidto a nontime varying (direct current) and substantially uniform appliedmagnetic field having a substantial component along the direction of theexternal force field (which will generally be gravity) such that thesolid particulate magnetizable and fluidizable material has a componentof magnetization along the direction of the external force field. As itwill be seen from the description of the invention and reference to thedrawings, the maximum superficial fluid velocity that can be employedwhile still maintaining a stable, nonfluctuating bed is a function ofthe component of magnetization of the solid particulate magnetizable andfluidizable material along the direction of the external force fieldwhich is imparted by the applied magnetic field. It is to be recognizedthat factors such as particle size, particle composition and shape,particle density, length and shape of the bed, etc. each affect themaximum fluidization velocity that can be achieved at a given componentof magnetization. The variation and adjustment of these factors will beapparent to those skilled in the art in practicing the process of thepresent invention.

The process of the instant invention enjoys benefits of solidsfacilitated for transport and limited pressure drop of a fluidized bedalong with absence-of-backmixing normally associated with fixed bedprocesses.

When fluid is passed upward through a bed of closely sized granularsolids, a pressure gradient is required to overcome friction. In orderto increase the rate of flow, a greater pressure gradient is required.When the pressure difference (also known as differential pressure andpressure drop Δ P_(o)) approaches the weight of the bed over a unitcross-sectional area, the solids begin to move. This motion of thesolids is created at superficial fluid velocities far below the terminalfree-settling velocities of the solid particles and constitutes thebeginning of fluidization. Thus, the normal minimum fluidizationsuperficial fluid gaseous or liquid velocity is the fluid velocityobserved when the pressure difference of the fluid passing through thefluidized bed, as measured between upper and lower surfaces of the bed,is first substantially the same as the bed weight per unitcross-sectional area. As is well known, superficial fluid velocity is ameasure of the linear fluid velocity that would pass through an emptyvessel and it is measured in feet per second, centimeters per second,etc. This point of normal minimum fluidization superficial fluidvelocity in the absence of an applied magnetic field is the minimumfluidization superficial fluid velocity of the process of the invention.

For solid particulate magnetizable and fluidizable materials, the pointof initial or minimum fluidization is not affected by the presence orabsence of an applied magnetic field. However, when the minimumsuperficial fluid velocity is exceeded in a bed which is not subjectedto the influence of an applied magnetic field, the porosity of the bedbegins to increase and the individual particles move under the influenceof the passing fluids concommitant with the formation of bubbles asshown in the left hand sketch of FIG. 1 of the drawings. Such a normallyfluidized bed experiences gross solids circulation, gas bypassing,bubble formation, slugging and bed fluctuation. By comparison, withapplication of a magnetic field in accordance with the practice of thepresent invention, the bed is stabilized, thereby reducing oreliminating: gas bypassing, bubble formation at the region or zone ofthe uniform magnetic field, slugging and bed fluctuation. Thus, agreater efficiency of fluid-solids contacting can be accomplished byoperating the process of the present invention.

As further illustration of the present invention, the phenomenon ofnormal fluidization can be visualized in terms of a simple experiment bythe left hand sketch of FIG. 1 in which a bed of solid particles issupported on a horizontal porous grid in a vertical tube. A fluidizingfluid in the form of a gaseous medium or liquid is then forced to flowupwards through the grid, and so through the particle bed. This flowcauses a pressure difference (pressure drop) across the length of thebed, and when this pressure difference is sufficient to support theweight of the particles, the bed is "incipiently fluidized" (thesuperficial fluid velocity required to attain incipient fluidization isthe "normal minimum superficial fluid velocity"). The fluidized bed thusformed has many properties of a liquid; objects float on the surface andthe addition or withdrawal of solid particles in process equipment isalso facilitated. As shown by the left hand sketch in FIG. 1, agas-fluidized bed in which the gas velocity is greater than theincipient gas velocity, most of the excess gas passes through the bed asbubbles.

By providing the solids of the bed with magnetizability and applying auniform, time-steady magnetic field oriented parallel with the directionof gas flow as shown in the right hand sketch in FIG. 1, it has beenfound that a stabilized non-fluctuating and essentially bubble-freefluidized bed results over a substantial range of superficial gasvelocities. As shown in the sketch in FIG. 1, the magnetic field may beconveniently furnished by wound coils carrying a modest direct electriccurrent and surrounding the fluidization vessel.

Referring to FIG. 3 of the drawings, there is an illustration of theresponse of magnetized solids to increase of superficial gas velocityfor a constant intensity of applied magnetic field. The solid particlesare a closely graded range of nickel-copper alloy (Monel). Measurementsof a particulate sample with a vibrating sample magnetometer yieldmagnetization values of 372 gauss at 5000 oersteds applied field, 326gauss at 3000 oersteds, 250 gauss at 1000 oersteds and 132 gauss at 200oersteds. The material is ferromagnetically soft with a remanence ofless than 5 gauss. With no gas flow the bed length is that of therandomly dumped solids. The bed comprises 2840 grams of the Monel(copper-nickel alloy) of 177-250 micron particle size and specificgravity of 8.45 in a vessel of 7.57 centimeter diameter with an appliedmagnetic field intensity of 5000 oersteds that is uniform over the testregion to within 1 percent. With a flow of air admitted to the vessel,the bed length is unchanging up to the point of incipient fluidization.Thereafter, the bed accommodates increasing flow by a process ofhomogeneous expansion in which detectable bubbles are not present in thebed and the bed of solids in gas emulsion is free of fluctuation,agitation or solids circulation. In this stable, calm state, a visualinspection of just the bed fails to reveal its fluid like nature.However, objects are readily immersed into the bed as into a liquid andwhen released light objects float and dense objects sink. A hollowplastic sphere of 3.72 centimeter diameter weighting 1.94 grams (pingpong ball) when initially rotated continues to spin for several seconds,thus indicating the very low frictional support it experiences whenfloating partly submerged in the bed emulsion. As the superficial gasvelocity (flow rate) is increased further, a point is ultimately reachedwhere bubbling suddenly commences. When the flow rate of gas is slowlyincreased to the vicinity of the transition point, the bed surface insome instances bubbles over part or all of its area for a limited time,then returns to the motionless state; apparently the medium adjusts to anew structure. A small incremental increase in throughput then producessteady bubbling and bed fluctuation. This flow rate is taken as theexperimental transition point. The uncertainty introduced into thereported values in this manner is on the order of 5% or less of thesuperficial gas velocity. As shown by FIG. 3, this point of transitionfrom the calmed or stabilized state of flow to the state of bubbling andbed fluctuation occurs at substantially higher flow rates than for theunmagnetized bed. As shown in FIG. 3, no expansion occurs until thevicinity of U_(MF), the minimum throughput velocity causing bubbling inthe absence of the applied magnetic field. Expansion continues as gasflow increases with no bubbling, bed fluctuation or solids mixing up tothe point U_(T), the transition speed. It was found that the transitionvelocity increases as the bed length decreases. When this Monelcontaining expanded bed length is greater than 100 mm, the transition isindependent of bed length and exceeds incipient fluidization velocity bya factor of 2.3 at the applied field of 5000 oersteds. At bed lengthless than 50 mm, the transition speed increases steeply as depthdecreases, e.g., 4.6 times greater than the incipient velocity at about20 mm length. Additional experiments have shown that the transitionvelocity of a stabilized bed is unaffected by the crosssectiondimensions of the containing vessel for tests in which the hydraulicdiameter varied from 3 to 28 centimeters.

When the transition velocity is determined by the method described abovefor a number of different applied field intensities, the resultsobtained give the plot of FIG. 4 of the drawings (FIG. 2 which issimilar to FIG. 4 is discussed further with respect to the examples).The experimental system used to provide the data in FIG. 4 is the sameas that used in FIG. 3 described above. The bed depths may be read fromFIG. 3. FIG. 3 defines three regions that classify the physical state ofthe bed emulsion as `unfluidized`, `stably fluidized,` or `unstablyfluidized.` The boundary between `stably` and `unstably fluidized`represents the transition described previously while the boundarybetween `unfluidized` and `stably fluidized` states represent incipientfluidization. As will be demonstrated in the Examples, the incipientfluidization is affected little or none by the applied magnetic fieldintensity. For example, bed pressure difference initially is linear withflow rate, then breaks at the point of incipient fluidization withpressure difference (pressure drop) about constant and closely equal tothe bed weight per unit cross-sectional area. The slope of the initiallinear portion of the curve is independent of applied field and it ispredictable from the low velocity limit of the well known fixed bedErgun relationship. The invariance of the plateau pressure level to thepresence of the applied field verifies the force free nature of theuniform magnetic field. Since the incipient fluidization pointcorresponds to the intersection of the said two lines, it follows thatincipient fluidization is independent of applied magnetic fieldintensity.

With velocity considered as analog to temperature or agitationinfluence, and applied field as analog pressure, FIG. 2 and FIG. 4resemble a thermodynamic phase diagram of a pure substance having solid(unfluidized or fixed bed), liquid (stably fluidized) and vapor(unstably fluidized or boiling) regions. This two phase magnetized flowin effect constitutes an aggregate composition of matter having uniquethermodynamic and transport properties.

Uniformity of the emulsion can be inferred from pressure measurementsusing a capillary tube connected to a manometer and inserted verticallyinto the bed. It is found that pressure increases linearly with depthimplying that voidage is uniform from one layer to the next throughoutthe bed.

Orifice discharge tests confirm the ability to transfer solids out ofthe containing vessel. The flow rate of the solids is characterized by aconstant value of discharge coefficient independent of applied fieldintensity or initial depth of the bed. Additional tests using bands ofsurface pigmented solids as a color tracer demonstrate that solids movethrough the bed in ideal piston-like motion with no backmixing when aseries of eight evenly spaced orifices are simultaneously opened arounda circumference of the vessel cylindrical wall a short distance abovethe support grid. The plug nature of the flow is participated in by allthe bed particles, including those adjacent to the wall. In thisrespect, the bed emulsion behaves as an inviscid medium displaying slipat the wall. At a distance on the order of the vessel diameter above theorifices the flow must devitate from simple one-dimensional motion.

It has been found that orientation of the applied magnetic field iscritical in achieving stable flow with the preferred direction colinearor parallel with the direction of flow and hence vertical in theseexperiments. Experimental tests using a uniform transverse orientationof applied field reveal that fluidization is achieved but bubbling isnot prevented, the bubbling occurring at the same throughput rate as inthe absence of the applied magnetic field, that is at incipientfluidization. These experiments comprised an applied magnetic field of570 ± 20 oersteds over a short bed of 150-420 microns nickel-on aluminaparticles of specific gravity 1.3 with bubbling occurring at 2.8 to 2.6cm/s with and without the field. Applying 520 oersteds field parallelwith the flow deferred transition to the extraordinary value of 43 cm/s;the bed expanded by 68 percent of its initial length.

In putting the present invention into practice, the substantiallyuniform constant magnetic field is applied to at least a portion or azone of the fluidized bed containing magnetizable, fluidizable solidparticles. The portion of the bed or series of beds to be stabilized maybe designed to suite the particular process to use the process of theinvention. For example, in some fluidization processes, it may beexpedient to stabilize the uppermost 10-40% or 1/3 region or zone of thebed while purposely allowing the remaining region or zone of the bed tobe unstable. Alternatively, the fluidization vessel may be disposed ofseparate and discrete sections, at least one of which is stabilized bythe process of the present invention. In both of such instances, it ispreferred that the region is stabilized by the applied magnetic fieldhaving a variation of its vertical component that does not exceed 25% ofthe average vertical component over the region or zone of the bed to bestabilized, said region containing the particulate magnetizable andfluidizable material. Preferably, the magnetic intensity will vary nomore than 10% and more preferably no more than 5% over the stabilizedregion. Often, it will be deemed desirable to design such regions orzones to have only about a 5% or less variance.

In many processes it will be desirable that the entire fluidized bed ina fluidization vessel be stabilized in accordance with the teachings ofthe present invention. In such cases, the widest range of stablebehavior of the fluidized medium is obtained when the applied magneticfield is substantially uniform throughout the entire bed containing themagnetizable and fluidizable solid particles. Thus, when the magneticfield is applied having a substantial vertical component to stabilizethe fluidized medium, the variation of the vertical component of themagnetic field to the mean field in the bed must be no greater than 50%,and most preferably no greater than 10%. Often, such fluidization unitswill be designed to have a less than 5% variation over the mean.

As demonstrated in Table IX, Example 7 below, it has been unexpectedlyfound that nontime varying vertical fields are preferred and provideadvantages over time varying fields, that is direct current (DC) ratherthan an alternating current (AC) is used to energize the electromagnetpositioned to provide the vertically oriented magnetic field. Anotheradvantage of uniform field is reduction of magnet power. Because thepower requirements for a given mean field are less with more uniformmagnetic fields, it is preferred that variation of the varying magneticfield to the mean field in the bed be no more than 100%, more preferablyless than 50%, and most preferably less than 10%.

Generally, it will be shown that the greater the uniformity of theapplied field, the greater will be the tendency to form a homogeneousbed medium and one which yields the greatest value of transitionvelocity. This fact furnishes the primary reason for utilizing uniformfields. Certain specific adverse influences of nonuniform fielddistribution are illustrated in Examples 3, 6 and 8 below.

A spatially uniform DC field having a superposed AC component behavessubstantially as a DC field provided the DC field intensity issubstantially greater than the amplitude of the AC field component.

The solid particulate magnetizable and fluidizable particles to be usedin the practice of the present invention are preferably particles havinga low or zero coercivity. All ferromagnetic and ferrimagneticsubstances, including but not limited to magnetic Fe₃ O₄, γ-iron oxide(Fe₂ O₃), ferrites of the form XO.Fe₂ O₃, wherein X is a metal ormixture of metals such as Zn, Mn, Cu, etc.,; ferromagnetic elementsincluding iron, nickel, cobalt and gadolinium, alloys of ferromagneticelements, etc. may be used as the magnetizable and fluidizableparticulate solids. Other non-magnetic materials may be coated withand/or contain dispersed therein solids having the quality offerromagnetism. For example, composites of magnetizable and fluidizablesolid particulates, for example in some catalytic processes may containfrom 2 to 40 volume percent and preferably 5 to 20 volume percent andmore preferably 10-15 volume percent of the ferro- or ferrimagneticmaterial and the balance of the composite will be comprised ofnonmagnetic material. Often it will be desirable to use a ferro- orferrimagnetic composite with a nonmagnetic catalytic material. Thefluidized bed containing the composites may also include particulatesolids which are nonmagnetizable. In other processes it may be desirableto use 100% ferro- or ferrimagnetic materials as the particulate solids.

An important factor in selecting or preparing the magnetizable andfluidizable particulate solids is the magnetization M of the particle.The higher the magnetization M of the particle, the higher will be thetransition velocity U_(T) up to which the bed may be operated withoutbubbling and bed fluctuation, all other factors such as particle sizeand distribution being held constant. The magnetization of themagnetizable and fluidizable particles in the medium will have amagnetization M of at least 10 gauss. Generally for high fluidvelocities, the particles will have a magnetization, as being impartedby the applied magnetic field, of at least 50 gauss, preferably at least100 gauss and more preferably at least about 150 gauss, e.g., 150-400gauss. For those processes requiring very high fluid velocities, themagnetization of the magnetizable, fluidizable particles may be up toabout 1000 gauss or more, but preferably 150-450 gauss.

The magnetization M of the particles, as is well known, is defined asB-H in the particle, where B is the magnetic induction and H is themagnetic field, the fields being defined in standard published works inelectromagnetism, e.g., Electromagnetic Theory, J. A. Stratton,McGraw-Hill (1941). The value of M may be measured in a variety of ways,all of which give the same value M since M has an objective reality.

One means for determining magnetization M of the particles in a bedunder the influence of a given applied magnetic field is to measuretheir magnetic moment at that field in a vibrating sample magnetometerunder conditions of similar voidage, sample geometry and temperatures asexist in the process to be used. The magnetometer gives a value of σ,the magnetic moment per gram from which magnetization M is obtained fromthe formula:

    M = 4 πρσ

where ρ is the density of the particles in the test sample, σ is themagnetic moment in emu/g and M is the magnetization of the particles ingauss at the applied magnetic field tested.

Thus, it can be seen from the above discussion that the fluid velocityregion of stable operation is potentially expanded with increasingmagnetization of the particles. The actual magnetization of theparticles in the fluidization vessel will be a function of the particlesthemselves (the degree of magnetizability they inherently possess) andthe intensity of the applied magnetic field.

As stated above the magnetizable particles should have a certain degreeof magnetization M which is imparted to the particles by the intensityof the applied magnetic field. Obviously one would seek the lowestapplied magnetic field possible because of cost. Commonly many of thecomposite particles will require at least 50 oersteds, more often morethan 100 and preferably less than 1000 oersteds to achieve the requisitemagnetization M. The determination of the applied magnetic field willtake into account the type of particles fluidized, i.e., theirmagnetization, particle size and distribution, the fluid velocity to beused, etc.

As stated earlier the magnetizable and fluidizable particles may beadmixed with nonmagnetic materials. For example, silica, alumina,metals, catalysts, coal, etc. may be admixed with the magnetizable andfluidizable particles and the advantages of the present invention stillobtained. In the case of admixtures (as opposed to composite materialscontaining the magnetizable particles) it is preferred that the volumefraction of magnetizable particles exceed 25 percent, more preferablyexceed 50 volume percent. Often the bed will be comprised of 100 volumepercent of the magnetizable and fluidizable particles (i.e., it will notcontain admixtures of other materials). When the nonmagnetizableadmixture exceeds 75 volume percent, the particle mixtures may separateanalogous to liquids of limited solubility.

The particle size of the fluidizable and magnetizable particles willrange from about 0.001 mm to 50 mm, more preferably from 0.05 to 1 mm.Often the particle size will range from about 0.05 to 0.5 mm, preferablyfrom 0.1 to 0.4 mm and more preferably from 0.2 to 0.35 mm. The particlesize range referred to herein is that determined by the mesh openings ofa first sieve through which the particles pass and a second sieve onwhich the particles are retained.

The superficial fluid velocity to be used in practicing the inventionwill be more than the normal minimum fluidization superficial fluidvelocity of the bed containing the solid particulate magnetizable andfluidizable material in the absence of the applied magnetic field.Preferably the superficial fluid velocity will be at least 10% above thenormal minimum fluidization superficial fluid velocity of the bedcontaining the solid particulate magnetizable and fluidizable materialin the absence of the applied magnetic field. In some instances it willbe desirable to operate the process at more than 2, 5, 10, 15 and 20 ormore, and quite often 2 to 10 times the normal minimum fluidizationsuperficial fluid velocity required to fluidize the bed containing thesolid particulate magnetizable, fluidizable materials in the absence ofthe applied magnetic field.

As the transition superficial velocities are increased the component ofmagnetization of the solid particulate magnetizable and fluidizablematerial along the direction of the external force field will have to beincreased so as to prevent time-varying fluctuations of pressuredifference through the bed during continuous fluidization. It will berecognized that particles of high magnetization such as iron and steelcan achieve a very high component of magnetization M at relatively lowapplied magnetic fields. These particles, however, have the limitationthat at applied magnetic fields, e.g., above 50 or 100 oersteds, theparticles tend to aggregate and take the form of a slug. Consequently,the level of superficial fluidization velocity that can be achieved withsuch particles is limited while still maintaining a non-fluctuating bed.The maximum useful levels for the magnetization M of most particles mustbe limited to about 500 to 1000 gauss in order to achieve a reasonablyfluid-like bed medium without undue agglomeration of particles. It canbe calculated that for iron spheres (which is approximately similar toparticulates used by Sonoliker et al. and Ivanov et al.) in a bedsubjected to an applied field of 50 oersteds the maximum magnetization Mof bed particle is about 300 gauss. However, it will be recognized thatat points of contact of the particles, the magnetization can be fargreater and hence the magnetic forces of agglomeration are greater.

The occurrence of bed fluctuation as referred to herein furnishes ameans of determining the transition superficial fluid velocity. Forexample, fluctuation of a fluidized bed can be determined by a varietyof techniques which measure the fluctuation of a bed property. Thus, bedlength fluctuation can be ascertained by a Hall probe placed in saidbed, by reflection of a light beam, etc. A convenient means fordetecting bed fluctuation is by determining the pressure differencethrough the bed containing the solid particulate magnetizable andfluidizable particles. For present purposes a time-varying fluctuationof pressure difference through the stably fluidized bed portion will betaken as indicative that the superficial fluid velocity has caused thatportion of the bed to go into the unstable region as shown in FIGS. 2and 4, i.e., the region beyond U_(T). Preferably, the superficial fluidvelocity will be less than 98% and more preferably less than 85% of thesuperficial fluid velocity necessary to cause fluctuations of the stablyfluidized bed-portion pressure-difference. A fluctuation in the pressuredifference in the bed is indicative of bubble formation, and it is theintent of the present invention to operate a fluidized bed in thesubstantial absence of bubbles. It will be recognized, of course, that anon-fluctuating fluidized bed in accordance with the practice of thepresent invention may contain some localized bubbles which aredissipated by the effect of the magnetic field to thereby cause bedstabilization. Such bubbles may be due to the presence of distributionmeans for introducing or removing fluids or solids from the fluidizationvessel, the presence of obstructions of the flow, momentary pulses inflow rate of the solids or fluid in the vessel etc. In any event, thesuperficial fluid velocity should be controlled or monitored such thatit is less than the superficial fluid velocity required to causetime-varying fluctuations of pressure difference through the stablyfluidized bed portion over a finite period of time, e.g., 0.1 to 1,preferably 1 to 10 seconds, and more preferably 10 to 100 secondintervals during continuous fluidization. The term fluctuations ofpressure difference through the stably fluidized bed portion, asreferred to herein, is meant to be restricted to those fluctuationsattributed to the fluidization process itself as a result of the fluid,i.e., gaseous material causing the fluidization, and not externalsources of vibrations which may cause minor fluctuations of pressurereadings, e.g., motors, fans, pumps, or due to the grid in the bed, etc.

In determining the pressure difference through the stably fluidized bedportion as defined herein, it is meant to include those measurementstaken in the uppermost region or zone of the stably fluidized bed, i.e.,the uppermost 20%, preferably uppermost 1/3 and more preferablyuppermost 40% region or zone that is stably fluidized. Thus, in testingfor fluctuations in pressure through the stably fluidized bed portion,one can determine these fluctuations if any, by measurement ofdifferential pressure and its fluctuation between two pressure taps, onelocated above the top surface of the bed and a second one located 20%,1/3 or 40% below the top surface of the stably fluidized bed portion. Inthose cases where it is desired to obtain a stably fluidized bed portionat the lowermost region of the entire fluidized bed, the measurementswould obviously be taken at this portion of the bed, i.e., one pressuretap at the grid and the other pressure tap 20%, 1/3 or 40% above thegrid. Additionally, where the stably fluidized bed portion is centrallylocated, one can determine the differential pressure and itsfluctuation, if any, between two pressure taps, one located 10%,preferably and more preferably about 1/6 and more preferably 20% of thetotal bed length above the center of the entire fluidized bed and theother pressure tap located an equal distance below the center.

The ratio of root mean square (rms) to mean value of pressure differencethrough the bed as detected by a pressure probe furnishes a convenientmeans to measure the presence of fluctuation within the bed.

Letting ΔP₁ be denoted as the difference between ΔP and ΔP_(o) where ΔPis the instantaneous value of pressure difference through the bed andΔP_(o) is the time mean value of pressure difference through the bed,then the quantity ΔP_(rms) defined as follows is the "rms" value ofpressure fluctuation ##EQU1##

Thus the ratio of rms fluctuation to the mean is given as ΔP_(rms)/ΔP_(o). As a practical matter, the averaging time T need only be takenas about 10 to 100 seconds duration of continuous fluidization.Preferably, in the operation of the instant process the flow of thefluidizing fluid is not substantially more than about 98%, morepreferably 95% and still more preferably 85% of the superficial fluidvelocity required to cause a 0.1% ratio of root mean square fluctuationof pressure difference to mean-pressure difference through the bedduring continuous fluidization.

It is to be understood that the value of 0.1% is not to be construed asthose attributed to fluctuations of pressure difference readings due tothe grid, distributor means for introducing or removing fluids or solidsfrom the fluidization vessel, etc.

THEORY OF THE INVENTION

While not wishing to be bound by any theory, the following theoreticalexplanation is offered for the purpose of further illustration of theinvention.

Hydrodynamic stability analysis has revealed that the uniformlymagnetized medium in a long bed undergoes transition from the stablyfluidized state in which there is no bubbling to the unstable bubblingstate of motion under conditions specified by the following stabilitycriterion which has been derived.

    ______________________________________                                                        >1          unstable                                          N.sub.M N.sub.v                                                                               <1          stable                                            ______________________________________                                    

The criterion for stability when met ensures that chance disturbance ofvoidages in the medium will decay so that uniformity of the medium ispreserved. N_(M) and N_(v) are dimensionless groups having the followingdefinitions: ##EQU2## N_(M) represents a ratio of kinetic energy tomagnetostatic energy of the bed solid; ρ is particle density (g/cm³), Uthe gas superficial velocity (cm/s), and M denotes solids magnetization(gauss). M is a function of applied field H attaining a saturation valueat high levels of applied field. N_(v), the voidage modulus, depends onthe voidage fraction ε_(o), the chord susceptibility χ_(o) = M/H, thetangent susceptibility χ = ∂M/ ∂H, the angle γ between the direction offlow and the direction of a wave disturbance and the orientation ofmagnetic field relative to the disturbance wave as specified by theangle θ.

For disturbance waves oriented along the direction of flow cos γ isunity and N_(v) takes on its greatest value, all other parameters heldconstant. Concomitantly, N_(M) takes on its least value at the point oftransition, so for a particle having given density ρ and magnetizationM, the velocity of througput U is then at a least value. Thus, the axialorientation of disturbance waves is the most dangerous orientation.

With cos γ set equal to unity the further influence of field orientationmay then be noted from the functional form of N_(v). Thus, field appliedtransversely to the direction of flow and hence corresponding to cos θof zero yields an infinite value of N_(v). In that case there is nofinite value of N_(M) which can satisfy the stability criterion, hence:transversely oriented field cannot stabilize the bed. The least value ofN_(v), all other parameters held constant, obtains with cos θ of unity.Hence, the preferred orientation of magnetic field is parallel with theflow direction, that is, vertically oriented. The stability criteriondiscussed above relates to a modelled bed of unbounded extent. Observedthroughputs for actual bounded beds range from "equal to" to "greaterthan" the estimate of throughput provided by the said criterion. Henceit will be understood that the instant invention is not meant to belimited by the said criterion.

Ideally the magnetic field should be uniform throughout the bulk of thebed containing the matter. A uniform field exerts no net force on anisolated single particle or a whole bed of particles. The stabilizationof matter achieved in the instant invention is due to local gradientfield magnetic forces originating within the bulk matter in response toinhomogeneities in bulk matter distribution that may occur. In practice,any actual applied field will possess nonuniformities. A sufficientlyuniform state of the stabilized matter when stabilization exists may beinsured by requiring systematic forces of magnetic origin to besufficiently small.

In seeking a universal description of the magnetic transition phenomenonin the bed of stationary solids, analytical model study as well asdimensional reasoning lead to the conclusion that for a long bed ofmagnetically saturated solids fluidized by a gas of negligible densitythe transition speed U_(T) (cm/s), particle density ρ (gm/cm³),magnetization M (gauss) and bed voidage ε_(o) are functionally relatedas follows:

    N.sub.m = f(ε.sub.o)

Here N_(m) is a dimensionless magnetic modulus representing a ratio ofkinetic energy to magnetostatic field energy having the followingdefinition:

    N.sub.m = ρU.sup.2 /M.sup.2

date for media 163,274 and 335μ Monel, and 53,270 and 335μ supportednickel in which voidage varies from 0.35 to 0.76 shown in the plot ofFIG. 7 support the above deduction and are approximately correlated bythe simple expression f(ε_(o)) = (3/2) ε_(o) ⁶ so that N_(m) = 3/2 ε_(o)⁶.

Referring again to FIG. 7, there is described the correlation oftransition modulus N_(m) with transition voidage ε_(o) which supportsthe theoretical conclusion of dimensional reasoning that a uniquerelationship exists between these two variables for magneticallysaturated, long beds. The supported nickel material has a density of1.30 g/cm³ and magnetization at 5000 oersteds applied magnetic field of228 gauss.

USES OF THE MAGNETICALLY STABILIZED FLUIDIZED BED

The fluidization process of the present invention may be advantageouslybe used in various applications, including but not limited to catalyticcracking, fluid hydroforming, isomerization, coking, polymerization,hydrofining, alkylation, partial oxidation, chlorination,dehydrogenation, desulfurization or reduction, gasification of coal,fluid bed combustion of coal, retorting of oil shale, etc. In any of theabove processes, the advantages of calm flow may be realized when thecomposition of matter of the instant invention is employed in the saidprocess.

In general, it has been discovered that the instant invention forpreparing stabilized, fluidized matter can readily be carried out in afluidized bed reactor comprising a vessel for containing the bed, a bedmade up of fluidizable particulate solids, said particulate solidsincluding a plurality of separate, discrete magnetizable particles, abed fluidizing medium, preferably a gas, and means for generating amagnetic field operably connected to said vessel in such a manner thatthe magnetic field permeates substantially the total volume of saidfluidized bed, is of a uniform nature, and is oriented with asubstantial vertical component to the flow of fluid through saidfluidized bed.

It is also found that the stabilized bed of the present inventionfunctions as an effective filter to remove contaminant particulates froma gas stream. The efficiency for collection of flyash in a 10 centimeterlength stabilized filter bed of 250-420 micron magnetite particles asmeasured by an Anderson impactor was found to be 99.9% and greater forparticulates of 4 microns and larger, and 95% for particulates of 2.1microns. An applied field of 150 oersteds with superficial gas velocityof 60 cm/s was used. Due to the fluidized state of the bed, the pressuredrop remains nearly constant in operation even upon collecting severalweight percent of fines. When the bed is loaded with fines, the contentsof the bed may be removed from the applied magnetic field to remove thefines and the magnetizable and fluidizable particles can be reused.

The stably fluidized bed of the present invention is useful in removingparticulate matter from fluid streams, including when the magneticmoment of the particulate matter times the magnetic moment of the solidparticulate fluidizable, magnetizable material is less than 50(emu/gr)².At these conditions the particulate matter is retained in the stablyfluidized bed, while the fluid stream is substantially devoid of theparticulate matter which passes through the stably fluidized bed. Thisembodiment of the invention is especially useful in treating gas streamsresulting from coal gasification processes, coal combustion, removal ofparticulates from boiler flue gases, removal of dust from agriculturalprocesses, blast furnaces and ore smelting, in petroleum processing, oilshale conversion, tar sand processing and other processes. Particulatematter removal using the stably fluidized bed of the present inventionis more effective than prior art processes for removal of fineparticulate matter down to sizes of less than 2 microns. In a preferredembodiment of this aspect of the invention, the solid particulatefluidizable, magnetizable material along with the particulate matterfiltered from the fluid stream are continuously removed from thescrubber vessel in which it is contained and passed into a second vesselwherein said particulate matter is separated from the solid particulatefluidizable, magnetizable material, for example by elutriating saidparticulate matter in the absence of an applied magnetic field. Theparticulate fluidizable, magnetizable material is then returned to thescrubber vessel. In one mode of operation of this aspect of theinvention, the scrubbing process takes place simultaneously with achemical reaction of absorption of pollutants from a gaseous fluidstream. As an example, a gaseous stream containing SO_(x) andparticulate matter convert the SO_(x) in the presence of carbon toelemental sulfur plus carbon dioxide in said fluidized bed at conditionswherein the particulate matter as well as any sulfur and/or carbon isretained in said bed while carbon dioxide passes through.

The following examples serve to more fully describe the manner of makingand using the above-described invention, as well as to set forth thebest modes contemplated for carrying out various aspects of theinvention. It is understood that these examples in no way serve to limitthe true scope of this invention, but rather are presented forillustrative purposes. It will be understood that all proportions are inparts by weight, unless otherwise indicated.

EXAMPLE 1

Ten grams of a ferromagnetic nickel-containing catalyst suppliedcommercially by Chemetron Corporation and known as Girdler G87RS wascharged to an open-topped rectangular fluidization chamber having innerdimensions of one inch by one and one-half inches over the crosssection, and a height of six inches above a porous bronze support grid.The catalyst had been crushed and sized by screening to the range 0.15to 0.42 millimeters. The catalyst is 40 wt. % nickel on a support withthe nickel prereduced and stabilized by the manufacturer. The dumpedheight of the solids was 22 millimeters.

Coaxially surrounding the bed was an electromagnet comprising two fieldcoils operating on direct current, wired in series and producing fieldin a common direction, both coils having an inner diameter of six inchesand square cross section of wound conductor of four inches, withface-to-face separation of the coils of 1.5 inches. The coils provided auniform, axially oriented field of 80 oersteds per ampere over a sixinch length of test region. The field was probed with a Hall gaussmeterand it was established that over the test region the field was uniformwithin ±5% of the mean value axially, and within ±1% over cross sectionstransverse to the flow direction. The midplane of the coils was located40 mm above the top of the bed support grid.

With no current supplied to the coil, hence at effectively zero appliedfield, the bed of catalyst particles exhibited incipient fluidization ata superficial velocity, i.e. volumetric flow rate divided by emptycolumn cross section of 2.6 cm/s. Before the superficial velocity wasincreased to 2.7 cm/s the bed bubbled continuously. Thus, theunmagnetized bed exhibits virtually no range of operation while in thefluidized state in which bubbles are absent.

In the test described above, the point of incipient fluidization wasdetermined by measurement of pressure differential across the bed asdetermined by an oil manometer connected to a pressure tap below the bedsupport grid and the readings corrected for the grid pressuredifferential determined without particles in the chamber. In thismanner, it was established that the pressure differential multiplied bythe bed cross-section area and divided by the weight of the bedparticles equalled unity in consistent units, as it should, at incipientfluidization, and that the pressure differential passed through acalculus maximum and then remained substantially constant at increasingflow rates.

The magnetic field was applied to the bed and the flow rate of airincreased from zero until the point where bubbling began, as determinedby visual observation. Transition to the bubbling state occurred at adefinite value of flow that is reproducible for each value of appliedfield intensity. A set of values determined in this manner is givenbelow as Table I.

                  TABLE I                                                         ______________________________________                                        Applied Field                                                                             Transition Superficial                                                                          Bed Depth,                                      Oersteds    Velocity, cm/s    mm                                              ______________________________________                                        0           2.6               23                                              125         21                29                                              280         27                34                                              400         34                36                                              520         43                37                                              680         51                37                                              ______________________________________                                    

From Table I it is seen that increase of the magnetic field increasedthe flow rate at which transition to the bubbling state occurred. At themaximum applied field employed of 680 oersteds, the transition flow rateof air was 19.6 times greater through the magnetically stabilized mediumthan through the medium of the unmagnetized, incipiently fluidized bed.

At flow rates intermediate to the incipient fluidization rate of 2.6cm/s and the transitional rates given in Table I, light objects, e.g., acork stopper or a hollow celluloid ball floated when placed in suchbeds. These objects, when submerged in a bed and then released,instantly were buoyed to the bed top surface, proving the fluidizedcondition of the bed in the absence of bubbling. Additionally, the ball,when spun, continued its rotation for several seconds, demonstrating alow level of frictional torque associated with the fluidized matter inthis stabilized mode of aggregation.

As flow is increased through the stabilized matter, the beds expand to aremarkable degree. Maximum expansion of the stabilized bed at thevarious applied field levels is given in the last column of Table I. Thebed exhibited an expansion of up to 66% of its as-dumped depth. Deepbeds are less expansive than shallow beds.

The instant invention comprises a new composition of matter exhibitingunique properties. FIG. 2 illustrates analog thermodynamic properties inthe form of a phase diagram. The ordinate U representing superficialvelocity, cm/sec or agitating influence is the analog of thermodynamictemperature T while the abscissa giving field intensities H is theanalog of thermodynamic pressure P. For concreteness, data of Table Iare employed to plot curve AB which represents values of superficialvelocity at the point of transition from the stable "liquid" state L tothe bubbling "vapor" state V. Thus, AB is analogous to the boiling pointcurve of a true liquid and the hydrodynamic neutral stability criteriongiving N_(M) N_(V) of unity is the analog of the Clausius-Clapeyronrelationship for thermodynamic phase change. Line AC represents theminimum fluidization speed and demarcates the region of fixed bed orsolid analog region S from the liquid analog region L. Thus line AC isanalogous to a melting point curve. The line from zero through A towardsD represents normal fluidization in the absence of field with bubblingoccurring virtually at the point of fluidization A, there being no rangeof stable operation. Operation at any field intensity with downward flowinsures attainment of the "solid" state S or fixed bed condition. Thusit is seen that region L represents a broad new regime within which thenew composition obtains and which offers a novel medium heretoforeunavailable for the contacting of gases with solids and for othertechnological tasks.

The new composition has a uniform bulk density and reference to columnthree of Table I illustrates that unlike normal fluidized matter thebulk density may be continuously adjusted simply by varying the flowrate of the fluidizing gas.

Transport properties of the new composition are unique as well. Forexample, heat conductivity is far lower than for normal fluidizedmatter. At the transition point the matter undergoes a change in thenature of a phase change becoming bubbling fluidized matter possessingdramatic increase in heat conductivity. Many other examples could becited of distinctive properties such as the rheological properties,electrical properties and so forth.

Later in Example 4 it is demonstrated that unlike normal fluidizedmatter but like a true liquid the matter of region L shows limitedsolubility effects.

EXAMPLE 2

In this example the direction of the magnetic field was transverse tothe direction of air flow. The field was provided by a pair of ceramicpermanent magnet plates having pole face dimensions of 6 inches by 3inches and each a thickness of 1/2 inch. Spaced 11/2 inches from face toface, these magnets produced a uniform magnetic field of 570 ± 20oersteds over the test region. The mid-plane of the magnetic plates waslocated 1 inch above the bed support grid.

The bed and bed solids were the same as in Example 1.

The response of this bed to increasing air flow rate is given in TableII below.

                  TABLE II                                                        ______________________________________                                        TRANSVERSE ORIENTATION OF FIELD                                               Field    Superficial Bed                                                      Intensity,                                                                             Flow Rate,  Depth,   Fluid-  Bub-                                    Oersteds cm/s        mm       ization bling                                   ______________________________________                                        570      0           22       No      No                                      570      0.6.sup.(a) 25       Yes     No                                      570      1.2         26       Yes     No                                      570      1.8         28       Yes     No                                      570      2.8.sup.(b) 29       Yes     Yes                                     ______________________________________                                         .sup.(a) The bed was levitated or fluidized as evidenced by the expansion     of the bed but the bed medium failed to float a test cork.                    .sup.(b) The bed exhibited violent slugging with chaotic flow at flow         rates in excess of 2.8 cm/sec.                                           

From Table II it may be seen that, in common with the case of Example 1wherein the field was vertically oriented, the magnetized bed expands agreat deal in response to increasing flow of the support gas, air.

Had the field of 570 oersteds been applied in the axial direction, theresults of Example 1 indicate by interpolation that transition tobubbling would not occur until flow rate equalled 45.5 cm/s, a flow ratethat is 16 times greater than the flow rate at which bubbling actuallyoccurred.

At all higher rates of flow in excess of 2.8 cm/s the bed exhibitedviolent slugging with chaotic flow. At all flow rates of less than 2.8cm/s the bed medium failed to float a test cork.

In accord with well-known principles of physics, a single magnetizableparticle placed in a uniform magnetic field experiences no net force. Inorder to experience a force, a magnetizable particle must be subjectedto a gradient of applied field magnitude. The instant inventionpreferably employs uniform applied magnetic field. As the result, whenvoidage nonuniformity tends to develop in the medium, the uniformity ofthe field is perturbed locally, and field gradients created that exertcorrective forces returning the medium to its initial state ofuniformity.

Gradient magnetic field in the horizontal direction can prevent themedium from achieving the state of fluidization, as illustrated inExample 3.

EXAMPLE 3 Effect of Transverse Magnetic Field Gradients

The 1 inch × 11/2 inch × 6 inch fluidization chamber with the G87RS bedparticles of Example 1 was subjected to the magnetic field of a ceramicpermanent magnet having the dimensions 2 inch × 1 inch × 3/8 inch withthe direction of magnetization through the 3/8 inch dimension. Themagnetic field of the magnet is given in Table III for various positionsalong the perpendicular from the center of the magnet's 2 inch by 1 inchpole face. The variation of magnetic field in the transverse directionacross the bed is about 168% relative to the mean field.

                  TABLE III                                                       ______________________________________                                        Position, s          Magnetic Field, H                                        (1/4 in)             Oersteds                                                 ______________________________________                                        0                    420                                                      1                    340                                                      2                    220                                                      3                    150                                                      4                     90                                                      ______________________________________                                    

In the range of positions given, the gradient of field is nearlyconstant, producing a maximum body force in the direction transverse tothe flow of about 1.3 times the force of gravity. This force ratio wascomputed from the relationship (4πρg)⁻¹ MdH/ds with g = 980 cm/s², ρ =1.3 g/cm³, dH/ds in units of oersteds/cm, assuming the value M = 168gauss.

The magnet's 2 inch × 1 inch pole face was stationed in juxtapositionwith the outside of 1/4 inch thick walls of the vessel, at variousstations along the bed bulk. As the result, fluidization was preventedat all flow rates over the range 0 to 60 cm/s. The nonuniform appliedmagnetic field locked the particles against each other and the containerwall, preventing fluidization.

The utility of the magnetically stabilized composition is expanded usingadmixtures of magnetizable solids with nonmagnetizable particulates asshown in the next example. In the instant invention there is minimumtendency for the particles to segregate due to magnetic attraction ofthe applied field since the applied field is specified as preferablyuniform. As a result, mixtures may be fluidized and stabilized,exhibiting the transition behavior and bed expansion properties. Thus,such mixtures may be employed in stabilized bed processes in addition tobeds comprised of all magnetic particles.

EXAMPLE 4

Admixtures were prepared of the nickel impregnated catalyst having aparticle size range determined by screening of 0.18 to 0.25 mm with azeolite cracking catalyst having particle sizes less than 0.07 mm. Theadmixture was placed into the fluidization vessel described in Example 1to a typical depth of 25 mm. The field source of Example 1 was utilizedto provide specified levels of applied magnetic field. Flow rate and bedexpansion at the transition from the stably fluidized condition to thebubbling condition were noted. Results of the tests are given in TablesIV and V below.

                  TABLE IV                                                        ______________________________________                                        Transition Velocity of Admixtures (cm/s)                                      ______________________________________                                                 Applied Field (Oersteds)                                             Wt.% Magnetics                                                                           0       100     300    500    700                                  ______________________________________                                        100        2.5     7       21     33     37                                   75         3.0     4       12     19     24                                   50         <0.2    1        3      5      6                                   0          <0.2    --      --     --     --                                   ______________________________________                                    

                  TABLE V                                                         ______________________________________                                        Bed Expansion of Admixtures at Transition                                     (% of Initial Height)                                                                  Applied Field (Oersteds)                                             Wt.% Magnetics                                                                           0       100      300    500   700                                  ______________________________________                                        100        2       27       58     68    70                                   75         3       18       37     43    45                                   50         <1      10       18     22    23                                   0          22      --       --     --    --                                   ______________________________________                                    

Admixtures containing 25% by weight of magnetics did not remainhomogeneously mixed during fluidization. Such a phenomenon, resemblinglimited miscibility in liquid-liquid mixtures, must be determined on anindividual basis for any particular admixture of bed particles.

The utility of the magnetically stabilized compositions in applicationssuch as ab or adsorptive separation of vapor species, catalystutilization and regeneration, particulate filtration and subsequent bedcleaning, reaction of solids in moving beds and allied applications inwhich bed solids must be transported to and from the bed depend on thefluidized solids behaving as a medium capable of flowing in response toa pressure differential. The following example illustrates that thesolids in the instant invention are imbued with fluid-like properties toa degree that is extremely well suited for such transport.

EXAMPLE 5

A tall, cylindrical, fluidization vessel of transparent plastic havinginner diameter, d_(b), of 7.37 centimeters and wall thickness of 0.44centimeters was provided with a circular orifice having diameter, d_(o),of 0.83 centimeters. The orifice center was located 7.5 centimetersabove the top of the bed's porous support grid. Quantities of -40/+60mesh G87RS magnetizable solids were admitted to the bed for tests inwhich the initial bed depth L varied from 8.0 to 14.2 centimeters abovethe center of the orifice. The superficial air speed in all tests wasconstant at 15.6 cm/s. Surrounding the bed was the source of uniform,axially oriented magnetic field provided within the bore of the two sixinch I.D. electromagnets. The applied field in these tests was of equalintensity on both sides of the orifice. When the orifice was suddenlyopened by removing a plug, it was observed that the bed contents issuedas a well defined jet.

In a separate test with no fluidizing air flow, and with no appliedfield it was established that the powders jammed the orifice at once,and would not pass through of their own accord.

Table VI provides experimental results obtained for the discharge of thestabilized fluidized solids through the orifice. The time for the solidsto discharge to a level L_(o) of 4.0 centimeters above the orificecenter was determined using a stopwatch, and a discharge coefficient Ccomputed as ##EQU3## where T is the time interval and g = 980 cm/s², theacceleration due to gravity. It may be seen from the table that theorifice coefficient was constant at 0.14 to 0.15 independent of initialbed depth or applied magnetic field intensity over the range studied.

                  TABLE VI                                                        ______________________________________                                        Discharge Coefficient for Flow Through an Orifice                             Opening from a Bed of Magnetically Stabilized Fluid                           Solids                                                                                     Discharge Coefficient, C, Di-                                                 mensionless Applied Field                                                     Intensity                                                        Discharge Time. s                                                                            80 Oersteds 400 Oersteds                                       ______________________________________                                        9.5            --          .15                                                10.4           .14         --                                                 12.6           --          .15                                                16.0           .15         --                                                 16.4           --          .14                                                19.0           .15         --                                                 20.6           --          .14                                                ______________________________________                                    

The above example and Table show that the stabilized fluidized solidsflow in the manner of a liquid and hence are facilitated for transportbetween and within processing vessels. No prior art worker has reportedany measurement or experiment demonstrating this behavior. Prior to thepresent invention this behavior for the magnetically stabilized solidswas unknown.

COMPARATIVE EXAMPLES EXAMPLE 6

U.S. Pat. No. 3,440,731 of Tuthill provides an example teaching the useof an alternating magnetic field to stabilize a fluid bed. The Tuthillexample in common with the instant invention utilized an axialorientation of field colinear with the flow direction. However, theinstant invention is distinguishable from the Tuthill example inspecifying a nontime varying uniform magnetic field in order to obtainthe widest range of bed stabilization over a specified range of gasfluidization flow rates as a function of applied magnetic field.

Thus Tuthill repeatedly teaches that the magnetic field exerts a forceon the magnetizable particles. As already mentioned it is well knownthat a uniform magnetic field exerts no force on a magnetizable particlewithin said field. In no manner does Tuthill teach, show or suggest thata uniform field which exerts no force can usefully change fluidization.It is the new and entirely surprising discovery of this invention that anew and useful fluidized composition of matter may be achieved by use ofa uniform magnetic field which exerts no force. In direct contradictionto Tuthill it is a necessary condition that the magnetic field besufficiently uniform to exert little or no force in order to achievesaid new fluidized composition of matter. Failure to use a uniformmagnetic field will have the result that the field exerts a force on thefluidized matter, causing it to be nonuniform with undesirable effects.

To demonstrate the improved performance attendant to an increaseduniformity of field, the Tuthill apparatus was duplicated andcomparative tests performed as described in the following example.

An electromagnetic coil having an inner diameter of 2 in. and a squarecross section of 11/4 in. was fabricated of 14 gage copper wire. Whensupplied with 60 cycle current of 1.25 amperes, 3.9 volts were measuredacross the magnet's terminals. The magnet resistance was 0.76 ohms andthus the I² R power dissipated by the magnet was 1.2 watts. A Hall probepositioned 9/16 inch above the top of the coil measured a fieldintensity of 34 gauss. At the same position Tuthill reports a fieldintensity of 365 gauss, or about ten times the value found here. It iswell known that the field generated by a coil of a given conductorhaving a given geometry depends only on the power input. If it is takenas a fact from Tuthill's example, that his magnet also dissipated 1.2watts, corresponding to 0.8 amperes of current and resistance of 1.9ohm, his field should be smaller. It appears that the field intensityreported by Tuthill would require 10 times the current or 100 times thepower he reported. Most likely the Tuthill field intensity isoverstated.

Notwithstanding the above variance, a duplicate of the Tuthill bed wasprepared comprising one hundred and ninety-two grams of 1/8 in. diametercarbon steel balls charged to an open-topped cylindrical glassfluidization chamber having an inner diameter of 11/2 in. and a heightof 24 inches. At the lower end of the column the diameter was taperedand fitted with a gas inlet of reduced diameter. Near the bottom of thecolumn and supported by the tapered section were several layers of wovenstainless steel mesh having about 1/8 in. openings. The mesh layers werearranged with their grid axes in non-orthogonal alignment to serve as acombination support grid for the balls and as a distribution plate forthe fluidizing medium. As such this apparatus duplicated the apparatusof Tuthill.

The height of the settled bed of balls extended for 21/2 inches abovethe topmost layer of mesh.

The electromagnetic coil was supported coaxially with the fluidizationcolumn with the mid-plane of the coil at a height of 41/2 in. above thetop-most layer of mesh.

A rotameter fed by a regulated source of compressed air was provided tomeasure the flow rate.

The results of a series of tests that indicate the influence of fielduniformity on bed stabilization is summarized by Table VIII.

In the absence of an applied field the bed fluidized at a superficialvelocity of 8.7 ft/s as evidenced by motion of balls at the bed surface.At 9.2 ft/s the bed contents exhibited circulatory motion, rising at thecenter and descending at the walls. At 10.5 ft/s the bed slugged to aheight of 10 mm. With further increases of flow rate the bed contentscould be made to slug to any desired height within the column. The valueof 10.5 ft/s was adopted as a reference velocity, with the last columnof Table VII representing incremental increases in superficial velocityassociated with the application of the magnetic field.

With the magnet positioned above the bed the field nonuniformity was165% as detailed in Tables VII and VIII. A comparative test at thenonuniformity of 51% corresponded to positioning the magnet at the levelof the center point of the bed. An additional test at nonuniformity of11% utilized another magnet, one having a six inch bore and four inchlength.

In all cases, the application of magnetic field caused a deferral ofslugging to a higher value of gas throughput.

In the tests described the bed contents were observed to recirculateprior to the onset of bed slugging. Generally this recirculation isundesirable in applications of stabilized beds requiring a high degreeof staging or excellence of countercurrent contacting. It was suspectedthat the cause of recirculation was the low pressure drop of the supportgrid relative to the pressure drop f the bed. A grid of 100 mesh screendescribed in the example below was substituted for the 1/8 inch mesh ofthe Tuthill bed and cured the problem.

                                      TABLE VII                                   __________________________________________________________________________    INFLUENCE OF A.C. FIELD SPATIAL UNIFORMITY ON SLUGGING                        OF BED OF 1/8IN. CARBON STEEL SPHERES                                                              Superficial Velocity, ft/s                               Test  Mean Field,.sup.(b)                                                                  Nonuniformity                                                                         Slugging.sup.(a)                                         Reference                                                                           Gauss  of Field, %.sup.(c)                                                                   Motion                                                                              Velocity Increment                                 __________________________________________________________________________    4391-14                                                                             0      --      10.5  0                                                  4391-15                                                                             35     165     12.0  1.5                                                4391-19                                                                             36     51      13.4  2.9                                                3459-51                                                                             35     11      14.4  3.9                                                __________________________________________________________________________     .sup.(a) 10 mm height.                                                        .sup.(b) Mean Field = (Maximum field in bed + Minimum field in bed)/2.        .sup.(c) Nonuniformity of field = (Maximum field in bed - Minimum Field i     bed) × 100/Mean Field.                                                  (d)Corresponds to nonuniformity in example of Tuthill.                   

                                      TABLE VIII                                  __________________________________________________________________________    MAGNETIC FIELD PARAMETERS                                                                                     Magnetic Field, Oersteds                                   Distance of Magnet                Non-                           Test  Magnet Center over Grid,                                                                       Magnet   Maximum                                                                             Minimum                                                                            Mean                                                                              uniformity,                    Reference                                                                           Identification                                                                       Inches    Current, Amperes                                                                       in Bed                                                                              in Bed                                                                             in Bed                                                                            %                              __________________________________________________________________________    4391-14                                                                             --     --        0         0.sup.(a)                                                                           0.sup.(a)                                                                          0.sup.(a)                                                                        0                              4391-15                                                                             2 inch bore                                                                          41/2      3        63.sup.(b)                                                                           6.sup.(d)                                                                         35  165                            4391-19                                                                             2 inch bore                                                                          11/4      1        45.sup.(c)                                                                          27.sup.(b),(d)                                                                     36  51                             3459-51                                                                             6 inch bore                                                                          11/4      .58      37.sup.(c)                                                                          33.sup.(b),(d)                                                                     35  11                             __________________________________________________________________________     .sup.(a) Ignores laboratory background field of about 0.5 gauss.              .sup.(b) Bed top surface.                                                     .sup.(c) Bed center.                                                          .sup.(d) Bed bottom.                                                     

Since Tuthill employed a magnetic source driven by an alternatingcurrent, the direction of field reversed with time. If the bed ofparticles possess an appreciable remanence the reversal of fielddirection can cause the particles to rotate or agitate in attempting totrack the field direction. The following example demonstrates theadverse influence alternating magnetic field can exert on stability ofsuch fluidized solids.

Example 7

The fluidization chamber of the example given previously was modified byremoving the coarse grid and adding a grid of 100 mesh screen capable ofsupporting powders that are screened to -40/+60 mesh. A packing of 1/4inch plastic spheres was provided upstream of the mesh to insure auniform approach flow. The first quadrant hysteresis loop for G87RSpowder was determined using a vibrating sample magnetometer. Thesaturation moment was 13.8 e.m.u./g. at 3500 gauss and remanence wasabout 3 e.m.u./g. A 39 mm depth of the G87RS powder was placed on thegrid and a series of tests performed using direct and then alternatingcurrent to energize the 11/4" × 11/4" cross-section magnet described inthe previous example. The results of these tests are summarized in TableIX. Here the term "transition speed" is used with a special meaning inreference to the AC tests wherein although the term denotes theobservation of surface bubbling the bed is not truly fludized (lifted).

                  TABLE IX                                                        ______________________________________                                        INFLUENCE OF ALTERNATING AND DIRECT                                           CURRENT FIELD SOURCES ON SURFACE                                              BUBBLING OF A MAGNETIC POWDER                                                 HAVING REMANENCE.sup.(a)                                                      Peak Field,.sup.(b)  Transition Velocity,cm/s                                 Gauss                DC           AC                                          ______________________________________                                        0                    13.0         13.0                                        30                   15.5         7.1                                         60                   17.8         7.8                                         90                   20.5         9.3                                         120                  22.4         10.0                                        ______________________________________                                         .sup.(a) 39 mm depth of -40/+60 mesh G87RS.                                   .sup.(b) DC and AC sources both 20% non-uniform over the bed volume.     

From Table IX it may be seen that application of the direct currentfield increased the transition velocity of the bed of powders whileapplication of the alternating current field decreased the transitionspeed relative to the value observed in the absence of field. Thus,alternating field is undesirable in preparing the said stabilizedcompositions of matter.

The instant invention is distinguishable from the Tuthill art in thattime steady magnetic fields are preferred in the instant invention.

Ideally in a fluidized bed an individual particle of the bed may rotatewith a minimum of frictional torque due to the negligible contact withneighboring particles. By considering the angular displacement of a bedparticle having remanent moment in response to the magnetic torque setup by a reversing field, with rotation resisted by particle inertiaalone, a criterion may be obtained indicating the range over whichalternating field produces an appreciable rotation of the particle andhence presumably tends to upset the stability of the bed. The criterionmay be stated as ##EQU4## The criterion applies for field cycle timesthat are smaller than the duration of bed operation. Thus, directcurrent beds, which have the greater stability, are not described by thecriterion. In the formula σ_(r) is remanent moment (e.m.u./g.), H isapplied field (oersteds), R is equivalent spherical radius of theparticle (cm) and f is frequency (Hz). Table X comparing conditions ofExamples 6 and 7 illustrates that the criterion predicts correctly theoutcome of these tests. Thus, the criterion is suggested to detireatethe combinations of particle magnetic moment and size, and magneticfield intensity and frequency which permit bed stabilization to beobtained in the face of alternating field. Stability in the race ofalternating applied field is favored by large particle size, highfrequency, and small remanence. As can be seen from the above Example,the use of alternating applied magnetic fields can be deleterious to thestability of fluidized magnetized solid particulates.

                  TABLE X                                                         ______________________________________                                        STABILITY OF FLUIDIZED SOLIDS TO ALTER-                                       NATING MAGNETIC FIELD                                                                      Example 6 Example 7                                              ______________________________________                                        Bed Media      Iron spheres                                                                              Catalyst powder                                    Particle size,                                                                R, cm.         0.16        .021                                               Remanent moment,                                                              σ χ, c.m.u./g.                                                                     1.5         3.0                                                Field intensity,                                                              H, oersted     35          30                                                 Frequency, f. Hz                                                                             60          60                                                 N.sub.c (computed)                                                                           0.13        11                                                 Prediction     Stable      Unstable                                           Observation    Stable      Unstable                                           ______________________________________                                    

Example 3 has already illustrated the very adverse influence that anappreciable transverse gradient of field may exert on the ability of abed of magnetizable particles to be fluidized. In the following example,it is demonstrated that when the applied field is vertically oriented itis preferable in the interest of achieving the widest possible stablerange of the bed at the lowest consumption of electrical power toutilize the most uniform possible magnetic field.

Example 8

Various configurations of magnets, magnet position relative to thevessel and magnet current were set up to provide discrete levels offield nonuniformity at several constant values of mean field appliedover the volume of a bed of -40/+60 mesh G87RS solids having a settledbed depth of 39 mm. The magnets were those described in the previousexamples. The bed was the 11/2 inch inner diameter glass column.

The operating conditions and test results are given in Table XI where itmay be seen that mean field was set as 0, 40 ca 120, or 400 oersteds inany given test and, likewise, the variation of field over the volume ofthe bed in any one test was established as 136%, 17% or 4%. Transistionspeed was established by noting for a bed whose content had previouslybeen aerated in the absence of applied field, the flow rate at whichsteady bubbling was observed at the top surface after magnetic field hadagain been applied. The last column of Table XI lists the width of thestable range, measured in velocity units, between the normalfluidization speed of the bed and the speed at which bubble transitionoccurs. At the low mean field of 40 oersteds where the stable range isvery narrow, about 4 velocity units (cm/s), the precision of the datadoes not permit any conclusion regarding the influence of fieldnonuniformity on transition. However, at the mean field of about 120oersteds it is seen that the field with 4% variation stabilizes twice asbroad as nonbubbling range as the nonuniform 17% and 136% cases. Thesame striking behavior is exhibited in the tests at 400 oersteds meanfield in which stability over a range of width 29.1 cm/s was achieved at4% spatial variation in applied field while 17% variation reduced thestable range to only 17.8 cm/s.

In addition to the superior performance attendant to use of uniformfield it is noted that power consumption to operate an electromagnetsource of field is vastly reduced. For example, referring to Table XI,for mean field of 120 oersteds, the equivalent stable range is obtainedat 136% nonuniformity as at 17%, but the power consumption assuming themagnet's resistance was unchanged, was larger by the square of the ratioof current. This computes to (25/3)² or 69.4 times the power consumptionat 136% as at 17% nonuniformity of field.

                                      TABLE XI                                    __________________________________________________________________________    INFLUENCE OF AXIAL D.C. FIELD AXIAL UNIFORMITY ON TRANSITION                  TO BUBBLING FOR BED OF -40/+60 MESH G87RS.sup.(b)                                   Magnet  Current,                                                                           Mean Field,.sup.(c)                                                                  Nonuniformity.sup.(c)                                                                  Superficial                                                                          Velocity,cm/s                       Test No..sup.(c)                                                                    Configuration.sup.(a)                                                                 Amperes                                                                            Oersteds                                                                             of Field, %                                                                            Transition                                                                          Stable Range                         __________________________________________________________________________    47:20 None    0.0  0      0        13.2  0.0                                  50:A  T/A     9.0  40     136      17.8  4.6                                  47:24 T/C     1.0  40     17       16.6  3.4                                  49:B  R/C     0.5  40     4        17.3  4.1                                  50:C  T/A     25.0 111    136      21.3  8.1                                  47:25 T/C     3.0  120    17       21.9  8.7                                  49:D  R/C     1.5  120    4        30.8  17.6                                 50:E  T/C     10.0 400    17       31.0  17.8                                 47:10 R/C     5.0  400    4        42.3  29.1                                 __________________________________________________________________________     .sup.(a) T denotes 2 inch bore 11/4" × 11/4" cross-section toroidal     electromgnet. R denotes two 6 inch bore electromagnets at 11/4 inch           separation. A denotes magnet center 41/2 inches above support grid. C         denotes magnet center coincident with center of bed.                          .sup.(b) Settled bed depth of 39 mm over 100 mesh grid.                       .sup.(c) Definitions are given in footnotes to Table VIII.               

Throughout the foregoing the discussion has utilized the artifice of afluidization chamber operated in the presence of a gravitational forcefield. It will be evident that the new composition of matter can begenerated as well in other force fields provided the flow of fluidizinggas is in the direction opposing the external force field. Thus theforce field may be due to centrifugal forces of a rotating system, orfor the electrical force on charged matter in an electrostatic field, orto dielectrophoretic force of electrically polarized matter in anelectrostatic field having a field gradient, or to forces caused bypresence of a magnetic field gradient, or to Lorentz force due topassage of a current at an angle to a magnetic field, or due to anyother force field or to combinations of the foregoing. In each instancethe end result is the achieving of a stable form of fluidized matterhaving the thermodynamic analog properties, transport properties andother properties inherent to the state of bulk matter already described.

It is noted that while the instant invention has been defined in termsof a novel composition of matter, the process for obtaining saidcomposition, as claimed below, is also a part of the instant invention.Also the composition of matter disclosed above may be arrangedthroughout the contents of a bed or alternatively, if desired, at pointsor regions within a bed. It will be understood that the term pointdenotes a localized region which in all dimensions is large compared tothe spacing between particles and is small compared to any dimensions ofthe bed.

Example 9

Example 5 demonstrated that the solids in the magnetically stabilizedfluidized bed will flow and discharge through an orifice in the vesselsidewall. The purpose of this example is to demonstrate further thatmovement of the solids may achieve piston displacement with no relativemotion between bed solids when the bed discharges.

Twelve hundred and eighty five grams of 350 to 840 microns G87RScatalyst was placed in a 7.5 centimeter transparent plastic vesselfitted with a porous disk distributor. The dumped bed height was about28.4 centimeters. Eight discharge ports were provided symmeticallyspaced around the vessel sidewall, each having diameter 0.64 centimeterwith the center of each hole 3.8 centimeter above the top of thedistributor. A rotary valve permitted opening the discharge portssimultaneously.

A portion of the normally black bed solids was tagged with a surfacecoating of blue pigment particles, Ultramarine 59-4933 of CyanamidCompany, and placed in the bed in layers. In the settled bed the bluecolored layers varied from 0.80 to 1.0 centimeter in thickness with thebottom of the lowest layer located 9.7 centimeters above the distributorand the remaining layers spaced 5.0 centimeters apart from each otherwith the uppermost layer forming the top of the bed.

The field source was a 20 centimeter bore by 100 centimeter longelectromagnet solenoid made up of 12 identical pancake modules eachhaving thickness of 4.1 centimeters and face to face separation of 7.0centimeters over the region occupied by the vessel. The applied fieldwas uniform to within 2% over the test volume, and in the test appliedfield intensity was constant at 400 oersteds.

With the field applied and the discharge ports closed, a flow of air wasadmitted to the vessel. As minimum fluidization speed was passed the bedexpanded with further increase of flow rate and the colored bands wereobserved to rise with the bed. The flow rate was brought to asuperficial velocity of 30.5 cm/s. The interfaces between the coloredlayers and the bed remained sharply defined.

The rotary valve was actuated to suddenly open the eight dischargeports. The bed volume then suddenly contracted due to reduction of airflow up the bed as a portion of the flow bypassed through the dischargeports. Then a slower process of bed movement continued in which thesolids descended and the colored layers were observed to move down thecolumn as bed solids discharged through the vessel sidewall openings.With the bed solids about half discharged the rotary valve was rapidlyclosed, the full upward flow of air resumed, and the bed observed toexpand and accommodate the increased air throughout that once again wasestablished.

With the bed then quiescent in stable batch operation, the coloredlayers could be examined at leisure. Inspection of the layersillustrated they were free of distortion and that the bed was free ofsolids backmixing insofar as could be detected from the appearance atthe bed side surface and the bed top. There was no adherence of solidsto the wall and it was concluded the solids descended with uniform speedover the bed cross section. Sufficiently close to the discharge portsthe flow, of course, cannot remain one dimensional in character but mustflow sideways.

Inspection of the solids discharged from the ports revealed the amountsto be closely equal and distributed in piles at nearly equal distancesfrom the discharge ports.

The rotary valve again was opened and the solids permitted to dischargefully. Motion picture photographs were recorded of the test and verifiedthe above description.

Example 10

The purpose of this example is to illustrate by measurement the absenceof fluctuations of bed voidage in the stably fluidized magnetized bed ofthe present invention and the presence of fluctuations when the bedbubbles.

One hundred and sixty six grams of -20/+30 U.S. sieve G-87RS catalystwere placed in a 5 centimeter I.D. glass vessel fitted with a porousdisk distributor. A magnetic field of 569 oersted intensity was appliedto the bed. Nitrogen at ambient temperature and pressure was passedupward at a superficial velocity of 51.4 cm/s yielding an expanded bedheight of about 15 centimeters. Minimum fluidization velocity previouslywas found to be 23.5 cm/s as determined from the breakpoint in a curveof measured values of pressure vs. flow rate.

A Hall effect gaussmeter probe (Bell Z OB4-3218) was mounted above thevessel with its active element in the middle of the bed of solids. Theprobe is a flat ended cylinder of 0.81 cm O.D. sensing the magneticfield component normal to the flat end, i.e. the axial component offield in the vessel. The probe was connected to a Bell 620 gaussmeter,whose output was amplified by a Tektronix AF 501. A custom low-passfilter having amplitude response down 50% at 70 Hz to eliminate a 5 KHzgaussmeter oscillator signal then fed a Disa 55 D 35 RMS unit operatedwith a 100 second averaging time, whose output was recorded on aHewlett-Packard 7004B X-Y recorder.

Table XII presents the sequence of mean axial magnetic field intensitiesapplied to the bed, the fluctuation of the field expressed as apercentage of the mean and the visually observed state of the bed.Fluctuations were absent within the precision of the measurement at meanfield intensities of 350 oersted and greater, corresponding to avisually observed quiescent state of the bed. The fluctuation levelrises very sharply as the field is decreased through the bubble point,and more gradually thereafter. The zero measured values of H rms/H meansin column 2 of Table XII indicate the complete absence of bubbles in thefluidized medium.

                  TABLE XII                                                       ______________________________________                                        MAGNETIC FIELD FLUCTUATION MEASUREMENTS                                       IN FLUIDIZED MAGNETIZED MEDIUM                                                Hall Probe Measurements                                                       H mean  H rms.sup.(1) /H mean                                                 oe.     %                State of Bed                                         ______________________________________                                        569     0                      quiescent                                      461     0                      quiescent                                      442     0                  .sub.(2)                                                                          quiescent                                      400     0                      quiescent                                      360     0                      quiescent                                      350     0                      quiescent                                      309     0.6                    light bubbling                                 242     1.0                    moderate bubbling                              119     1.8                    heavy bubbling                                  60     2.2                    heavy bubbling                                  12     5.0                    heavy bubbling                                 ______________________________________                                         .sup.(1) rms is defined as the root mean square of the fluctuation signal     .sup.(2) Values listed as zero in fact were somewhat less than the noise      level after correcting for measured noise, hence are neglected. The           neglected values ranged from 0.004 to 0.013 percent.                     

Example 11

This example demonstrates the influence of particle size and bed mass ontransition velocity.

The bed solids were various narrowly sieved sizes of Monel(ferromagnetically soft copper-nickel alloy) having specific gravity8.45 and particle magnetization of 372 gauss at 5000 oersteds appliedfield. The transparent plastic cylindrical fluidization vessel was 7.57centimeter inside diameter and fitted with a porous disk distributor.The fluidizing gas was air. The field source was the 20 centimeter boreelecctromagnet described in Example 9. This electromagnet was watercooled through its hollow copper conductive windings.

Results of tests in which length of the bed and superficial velocity ofthe air were determined at the transition point are tabulated in TableXIII for various amounts of solids in the vessel. At every testcondition the bed was observed to fluidize smoothly, the bed top surfacewas flat and finely structured, and transition to bubbling occurredsuddenly with a reproducibility of 5% or less of the superficialvelocity.

It may be seen that transition velocity increases with increase ofparticle size and decreases with increase of bed length. The transitionspeed of long bed tends to be invariant of bed length.

The response and expansion of a bed having a constant mass of Monelsolids is given at Table XIV. As superficial velocity increases from itsinitial zero value the bed remains unchanged in length save for a minorrestructuring of the bed top surface. At the point of minimumfluidization the bed begins to expand. Expansion is continuous as flowrate increases with the medium remaining quiescent in the stablyfluidized state until the point of transition to bubbling occurs. Thebreak in the curve of bed length versus flow rate furnishes a definitivemeans of determining minimum fluidization speed as an alternative todetermining the break in the curve of pressure drop versus flow rate.

                                      TABLE XIII                                  __________________________________________________________________________    CORRESPONDING VALUES OF TRANSITION LENGTH                                     AND VELOCITY IN VARIABLE MASS BEDS OF MONEL                                           H = 5080 Oersteds                                                             Particle Size, Microns                                                Nominal Mass.sup.(1),                                                                 149-177  177-250  250-297                                             Grams   L.sub.T, cm                                                                       U.sub.T, cm/s                                                                      L.sub.T, cm                                                                       U.sub.T, cm/s                                                                      L.sub.T, cm                                                                       U.sub.T, cm/s                                   __________________________________________________________________________    150     2.2 93   2.6 130  2.2 124                                             400     --  --   5.6 90   5.0 115                                             700     7.1 51   7.5 70   7.9 94                                              1250    13.5                                                                              50   13.6                                                                              62   13.7                                                                              85                                              1900    19.2                                                                              50   19.9                                                                              64   20.0                                                                              85                                               .sup.(1) Minimum bubbling speeds in absence of field increase with bed        mass over the range given below:                                         

    D.sub.p, Microns    Velocity, cm/s                                                   149-177      19-22                                                            177-250      25-29                                                            250-297      33-42                                                     __________________________________________________________________________

                  Table XIV                                                       ______________________________________                                        RESPONSE AND EXPANSION OF CONSTANT MASS                                       MONEL SOLIDS TO INCREASING AIR FLOW RATE                                      Superficial Velocity,                                                                         Bed Length                                                    U, cm/s         L, cm      Comments                                           ______________________________________                                        0               20.7       Unfluidized                                        12              20.7       Unfluidized                                        18              20.8       Unfluidized                                        22              20.8       Unfluidized                                        28              20.8       Min. Fluidization                                  34              21.5       Stably Fluidized                                   40              22.3       Stably Fluidized                                   51              24.4       Stably Fluidized                                   57              25.5       Stably Fluidized                                   61              26.0       Stably Fluidized                                   66              26.3       Transition Point                                   Mass of Monel 2840 grams.                                                     Particle size 177-250 micron.                                                 Applied field 5000 oersteds                                                   Vessel I.D. 7.57 centimeters.                                                 ______________________________________                                    

Example 12

This example demonstrates that minimum fluidization velocity of amagnetizable particle bed is constant and unaffected by the presence ofintensity of an applied magnetic field and that a higher velocity of gasthroughput is required to cause the stably fluidized bed to undergotransition from the quiescent state to a state of bubbling or sluggingmotion.

A cylindrical fluidization vessel of 7.49 centimeter inside diameter and41 centimeter height over a microporous support grid is loaded with 3110grams of C1018 iron spheres supplied by Nuclear Metals Corporation. Theiron spheres are screened to the size range of 177 to 250 microns. Thebed length with initially loaded solids is 15 centimeters. The magneticfield source is the pair of 6 inch bore electromagnets, each havinglength of 4 inches and face to face separation of 1.5 inches. Themagnetic field is oriented colinear with the bed flow axis, with thecenter of the magnet pair at the center of gravity of the bed contents.The fluidizing gas is air.

A long straight glass tube of 6 mm O.D. and 4 mm I.D. is insertedvertically into the bed to sense bed pressure in the bed. The tube tipis positioned one centimeter above the bed grid and a U-tube manometerconnected to the other end of the tube. The bed is fluidized in thebubbling regime in the absence of field, then collapsed by stopping thegas flow before the beginning of a test sequence. The magnetic field isapplied in the absence of flow, and pressure measured in response toincreases in flow rate at the constant magnetic field setting.

Magnetometer measurement of the iron solids using the vibrating sampletechnique gives the values of magnetic moment listed in Table XV.

                  TABLE XV                                                        ______________________________________                                                 MAGNETIC MOMENT OF 177-250 MICRON C1018                                       STEEL SPHERES.sup.(1), (2) IN APPLIED FIELDS                         Applied Magnetic                                                                            Magnetic Moment                                                                             Magnetization                                     Field, H, Oersted                                                                           σ, emu/g                                                                              M, gauss .sup.(3)                                 ______________________________________                                         0            0.026         2.6                                               16            0.68          67                                                32            1.28          127                                               48            1.86          184                                               64            2.45          242                                               80            3.03          300                                                 0.sup.(4)   0.030         3.0                                               ______________________________________                                         .sup.(1) Sample mass of 0.3329 grams in cylindrical sample holder of abou     3 mm I.D.                                                                     .sup.(2) Saturation moment in 16,000 oersteds applied field of 212 emu/g      or 20,970 gauss.                                                              .sup.(3) M = 4 πρσ with density ρ taken as 7.87              gram/cm.sup.3.                                                                .sup.(4) Reduced from 80 oersteds.                                       

The remanent magnetization of 2.6 to 3.0 gauss is small compared to themagnetization values at the applied field intensities, hence thematerial may be regarded as ferromagnetically soft in this workingrange.

Table XVI lists values of pressure drop across the whole bed lengthversus superficial flow rate at various intensities of applied magneticfield. FIG. 5 presents the data plot for the field intensity of 48oersteds. The breakpoint of the curve is taken as the point of minimumfluidization. Values of minimum fluidization velocity U_(MF) obtained inthis manner are tabulated in the second column of Table XVII. There itmay be seen that minimum fluidization speed has a sensibly constantvalue independent of applied field intensity.

From column three of Table XVII it is seen that bed length is constantand unchanging below the point of minimum fluidization. The bed expandsat flow rates greater than minimum fluidization velocity, reaching thelength given in the fifth column of Table XVII at the point oftransition to the bubbling state. The transition to bubbling or sluggingoccurs suddenly as determined by visual observation. Steady surfacebubbling for a minimum duration of about 30 seconds is taken ascriterion for the transition, with the velocity at transition denotedU_(T). Values of U_(T) are tabulated in the fourth column of Table XVII.At H of 64 and 72 oersteds, transition was to slugging.

FIG. 6 presents the diagram that results from plotting U_(MF) and U_(T)versus applied field. The magnetically stabilized state of fluidizedsolids is defined by the region between the curves of U_(MF) and andU_(T). This region provides a broad operating range in which the mediumis fluidized yet quiescent and free of bubbles or solids backmixing. Thebed medium in this region is facilitated for transport, e.g. into or outof the containing vessel.

                  TABLE XVI                                                       ______________________________________                                        INFLUENCE OF FLOW RATE AND APPLIED FIELD                                      INTENSITY ON PRESSURE DROP FOR FLOW OF                                        AIR THROUGH A BED OF IRON SPHERES.sup.(1), (2)                                Flow Rate, U                                                                            Applied Field Intensity,H, Oersteds                                 cm/s      0      16      32    48    64    72                                 ______________________________________                                        1.88      --     0.54    0.65  0.57   0.60  0.61                              4.25      1.5    1.4     1.5   1.5   1.4   1.5                                6.75      2.4    2.1     2.4   2.4   2.2   2.2                                9.50      3.4    3.1     3.3   3.3   3.3   3.3                                12.3      4.5    3.9     3.9   4.4   4.3   4.3                                16.7      4.6    4.5     4.2   5.1   5.4   5.4                                17.9      4.6    4.6     4.3   5.1   5.7   5.6                                22.5      4.7    4.7     4.3   4.9   5.8   5.1                                25.3      4.6    4.6     4.8   5.1   4.6   5.3                                29.5      4.6    4.6     4.8   5.3   4.9   5.4                                35.1      --     4.6     4.8   5.3   5.4   5.5                                42.2      --     --      4.9   5.3   --    --                                 49.2      --     --      --    5.2   5.4   5.5                                70.0      --     --      --    --    5.2   4.8                                98.0      --     --      --    --    --    5.5                                ______________________________________                                         .sup.(1) Pressure units are centimeters of mercury, extrapolated to           support grid surface based on linear change with distance.                    .sup.(2) C1018 steel 177-250 microns.                                    

The final column of Table XVII tabulates the plateau value of pressuredrop normalized by the ratio of bed mass W to bed cross section area A;this quantity theoretically equals unity when expressed in dimensionallyconsistent units. The experimental values are in reasonable agreementwith the theoretical expectation and verify the existence of thefluidized state of the bed in both the stabilized and bubbling regimes,i.e. regions in which velocity U is less than and greater than U_(T),respectively.

Sonoliker, R. L. et al., Indian Journal of Technology, 10, 377 (1972)reported observations of fluidized iron powders subjected to an axiallyoriented applied magnetic field. In particular in Table I of Sonolikeret al., experimental results are given for the minimum fluidizationvelocity of iron particles, including results for particles of 244microns diameter, hence comparable to the size range studied here. Thevalues of minimum fluidization velocity in Sonoliker et al increaseexponentally with applied field intensity. This is in marked contrast tothe sensibly constant value of minimum fluidization velocitycharacterizing the instant invention and illustrated by values in columntwo of Table XVII below. It is possible that Sonoliker at al observedtransition velocity U_(T) and identified it as minimum fluidizationspeed U_(MF). Accordingly, Sonoliker et al might have passed through thestabilized region in a transitory manner in their experiments. In anyevent it is clear that Sonoliker et al provide no teaching of theexistence of a stably fluidized region as instantly claimed. In view ofthe report of Sonoliker et al the performance in the instant process andthe properties of the medium thereby generated are totally unexpectedand surprising.

                                      TABLE XVII                                  __________________________________________________________________________    BEHAVIOR SUMMARIZED FOR THE MAGNETIZED BED                                    OF STEEL SPHERES (177-250 MICRONS)                                            Applied Field                                                                        Minimum Fluidization                                                                     Bed Length At                                                                         Transition                                                                              Bed Length At                                                                          ΔP                         H, Oersteds                                                                          Velocity, U.sub.MF, cm/s                                                                 U.sub.mr, Lm, cm                                                                      Velocity, U.sub.T, cm/s                                                                 Transition, L.sub.T,                                                                   W/A                              __________________________________________________________________________    0      13.5       15.0    13.5      15.0     0.91                             16     14.8       15.0    25.8      15.5     0.89                             32     14.6       15.0    36.1      15.8     0.94                             48     15.6       15.0    49.2      16.8     1.00                             64     15.0       15.0    68.3      18.0     1.02                             72     15.0       15.0    68.3      --       1.00                             __________________________________________________________________________     At applied field of 80 oersteds the bed medium entrains as a plug moving      up the vessel column at a gas throughput less than transition.           

EXAMPLE 13

Ammonia catalyst of 3 to 6 mm. particle size was crushed and sieved toU.S. mesh -20/+30. This catalyst was previously magnetized in an appliedfield of 5000 oersteds. Due to its remanent magnetization the materialhad the texture of wet sand, noticeable when pouring or screening.

A quantity of 1280 grams was added to a fluidization vessel havinginside diameter of 7.33 cm. The depth of solids over the fitted porousdistributor was 17.8 cm.

In the absence of applied field as air flow was increased the bed ofsolids was observed to develop voidage layers of separation in the upperone-third of the bed at a superficial velocity of 10.3 cm/s. Pressuredrop through the bed increased smoothly with increase of superficialvelocity until at 38.3 cm/s a spout formed in the bed and the pressuredrop decreased from about 6.4 cm. of dibutylphthalate (DBP) to 2.9 cm.The spout had formed along the length of the 6 mm O.D. by 4 mm I.D.glass tube used as the pressure probe that was inserted at a 9 cm. depthwithin the bed. Thus, these solids failed to fluidize properly in theabsence of applied field.

When uniform, axially oriented magnetic field of 40 oersteds was appliedthe measured pressure drop increased smoothly with increase of air flowrate up to a superficial velocity of 42.7 cm/s. A further increase ofsuperficial velocity to 46.6 cm/s then caused a spout to form adjacentto the probe and the measured pressure drop decreased by about 47%.Again the bed structure deteriorated and lead to bypassing of the gasstream.

Finally, with applied field of 80 oersteds and the probe tip locatedabout 5 mm. above the support grid, the bed retained its structuralintegrity throughout a test sequence in which superficial velocityranged up to 100.4 cm/s. Pressure drop initially increased linearly withsuperficial velocity, then plateaued at 25.6 cm. DBP. The break in thecurve of pressure drop vs. superficial velocity defined a point ofminimum fluidization of 40.0 cm/s. The bed length was constant at 17.8cm. up to the point of minimum fluidization, then expanded to 24.0 cm.at the said maximum flow rate of 100.4 cm/s. The bed remained free ofbubbles or agitation at all flow rates studied. The test was repeatedand displayed the similar behavior with maximum superficial velocityreacing 115 cm/s.

Magnetic moment of this ammonia catalyst is given in Table XVIII. Theamount of 0.03 emu/g at zero applied field pertains to a powder sampleof the -20/+30 mesh material that had previously been subjected to 5000oersteds applied field. The low moment indicates the sample particleswere nearly randomly oriented since the remanent magnetization is largefor an undisturbed sample, i.e., 18.4 emu/g after exposure to appliedfield intensity of 16,000 oersteds.

                  TABLE XVIII                                                     ______________________________________                                        MAGNETIC MOMENT OF AMMONIA CATALYST                                           Applied Field H., re.                                                                           Magnetic Moment emu/g                                       ______________________________________                                        0                 0.03                                                        40                1.58                                                        80                3.26                                                        5,000             144                                                         16,000            166                                                         0                 18.4                                                        ______________________________________                                    

EXAMPLE 14

This example illustrates that fluctuations of gas pressure distinguishthe bubbling state of magnetized, fluidized solids from the stablyfluidized state. In the stably fluidized state fluctuations are notdetected.

Two thousand nine hundred and seventy grams of 177-250 micron sphericalparticles of C1018 steel described in Example 13 were placed in afluidization vessel having inside diameter of 7.32 centimeters. Thevessel was fitted with a pressure tap in the sidewall at a point 4centimeters above the porous support grid. The pressure tap contained awire mesh screen that prevented particles from leaving the vessel. Oneside of a U-tube manometer containing water was connected to the tap andthe other end of the manometer kept open to the atmosphere as was thetop of the fluidization vessel. Uniform, axially oriented magnetic fieldof 48 oersteds intensity was applied to the solids using the pair of sixinch bore electromagnets. Increasing rates of steady air flow wereadmitted to the vessel to obtain measurement of pressure drop ΔP_(o)read as difference in height of water in the manometer legs. When thebed became stably fluidized, its length gradually expanded withincreased gas flow. Observation was also made of pressure dropfluctuation ±ΔP', if any, and presence or absence of visible bubbling ormotion in the fluidized medium. The fluctuations in pressure droprepresent values detected over about a ten second interval. The observedvalues of pressure drop, pressure drop fluctuations, bed length andother parameters, are listed in Table XIX.

From the data in Table XIX it may be seen that the stably fluidizedstate is clearly distinguishable from the settled state (fixed bedstate) as well as from the unstably fluidized state. Thus, only in thestably fluidized state is pressure drop invariant of flow rate, and bedlength increasing with an increase of flow rate, while pressurefluctuations are absent. Comparative behavior of the states issummarized in Table XX.

It is noted that in the fluidized states the constant value of averagepressure drop indicates the solids in the vessel were supported entirelyby fluid forces. Visual observation of initial bubbling and motion inthe bed coincide with the first detectable fluctuation of pressure drop(pressure difference).

                                      TABLE XIX                                   __________________________________________________________________________    PRESSURE DROP, PRESSURE FLUCTUATIONS, AND BED LENGTH                          CHANGE OF AIR FLUIDIZED C1018 STEEL SPHERES OF 177-                           250 MICRON DIAMETER IN 48 OERSTED APPLIED FIELD                               U  ΔP.                                                                          ±ΔP'                                                                          State of                                                     cm/s                                                                             cm H.sub.2 O                                                                       cm H.sub.2 O                                                                       ΔL, cm                                                                      the solids                                                                              Bubbles or Motion                                  __________________________________________________________________________    5.6                                                                              19.1 0    0   Settled   No                                                 8.5                                                                              34.8 0    0   Settled   No                                                 12.7                                                                             54.0 0    0   Settled   No                                                 15.2                                                                             51.6 0    0.5 Stably Fluidized                                                                        No                                                 19.8                                                                             55.8 0    1.3 Stably Fluidized                                                                        No                                                 25.4                                                                             56.5 0    2.0 Stably Fluidized                                                                        No                                                 31.7                                                                             56.6 0.05 2.7 Unstably Fluidized                                                                      Yes                                                40.9                                                                             51.0 3.0  3.5 Unstably Fluidized                                                                      Yes                                                56.5                                                                             53.0 3.0  3.5 Unstably Fluidized                                                                      Yes                                                __________________________________________________________________________

                  TABLE XX                                                        ______________________________________                                        DISTINGUISHABLE                                                               STATES OF THE PARTICULATE SOLIDS                                              State         Pressure drop                                                                            Bed Length                                           of            increase   increase  Pressure                                   Solids        with flow  with flow Fluctuates                                 ______________________________________                                        Settled       Yes        No        No                                         Stably Fluidized                                                                            No         Yes       No                                         Unstably Fluidized                                                                          No         Yes       Yes                                        ______________________________________                                    

As can be seen from the above examples and description of the invention,the present invention provides a means for conducting a fluidizationprocess at a wide range of flow rates before the bubble transition pointis reached. For example, as discussed above, it has been found that thelarger the magnetization M of the fluidizable and magnetizible particlesup to the point of agglomeration, the higher will be the transitionvelocity U_(T) up to which the stably fluidized bed may be operatedwithout bubbling and time-varying fluctuation, all other variables beingequal. It will be recognized that in practicing the invention, it is theintent to operate the process in the stable, non-fluctuation mannerwherein the stably fluidized bed is bubble-free. Accordingly, the sizeof bubbles in the stabilized fluidized media, if they do exist, will beabout no larger than the spacing between particles and consequently donot cause time-varying fluctuations of the pressure difference throughthe fluidized bed over a finite period of time, e.g., 10 seconds,preferably a 100 second time interval during continuous fluidization.

As earlier indicated, the fluidization process of the present inventionis useful in many applications heretofore used in the fluidization art.Of particular importance are the petroleum processes such ashydrofining, hydrocracking, hydrodesulfurization, catalytic cracking andcatalytic reforming. The Table XXI summarizes typical hydrocarbonconversion process conditions effective in the present invention.

The feedstocks suitable for conversion in accordance with the inventioninclude any of the well-known feeds conventionally employed inhydrocarbon conversion processes. Usually, they will be petroleumderived, although other sources such as shale oil and coal are not to beexcluded. Typical of such feeds are heavy and light virgin gas oils,coker gas oils, steam-cracked gas oils, middle distillates,steam-cracked naphthas, coker naphthas, cycle oils, deasphalted residua,etc.

GENERAL

Generally, the magnetization M of a particle as obtained from amagnetometer when a given magnetizing field H_(a) is applied will notprovide a value which is the same as the magnetization of the particlein response to the same intensity of magnetic field in the fluidized bedto be used in accordance with the teachings of the present invention.

The purpose of the following is to indicate a method for determining themagnetization M_(p) of a typical particle in a bed from those valuesobtained from a magnetometer. Generally, this will require a calculationsince the effective field that a bed particle is subjected to depends onthe applied field, the bed geometry, the particle geometry, the bedvoidage and particle magnetization. A general expression has beenderived to relate these quantities based on the classical approximationof the Lorentz cavity that is employed in analogous physical problemssuch as the polarization of dielectric molecules.

    H.sub.a = H.sub.e + M.sub.p [d.sub.p + (1-ε.sub.o) (d.sub.b -1/3)](1)

H_(a) is the applied magnetic field as measured in the absence of theparticles, H_(e) the magnetic field within a particle, M_(p) theparticle magnetization, d_(p) the particle demagnetization coefficient,ε_(o) the voidage in the particle bed, and d_(b) the bed demagnetizationcoefficient. The term -1/3 is due to the magnetizing influence of a(virtual) sphere surrounding the bed particle.

The expression above applies as well to a sample of particles such asused in a magnetometer measurement. In that case d_(b) is thedemagnetization coefficient d_(s) corresponding to shape of the cavityin the sample holder.

Magnetometer measurement produces a graph of M_(p) vs. H_(a). Using theabove equation and known values of d_(p), d_(s), ε_(o), M_(p) and H_(a)a corresponding value of H_(e) may be computed. When the value of H_(e)is small its value found in this manner is determined by a differencebetween large numbers, hence is subject to cumulative errors.Accordingly, a modified approach is useful as described in thefollowing.

Thus it is useful to define a reference quantity H_(s) representing thecalculated field in a spherical cavity at the location of the particle.It is imagined that the magnetization of surrounding particles isunchanged when the said particle is removed.

    H.sub.s = H.sub.a - M.sub.p [(1-ε.sub.o) (d.sub.b -1/3)](2)

Combining the two expression gives an alternate relationship for H_(s),in which H_(a) is eliminated.

    H.sub.s = H.sub.e + M.sub.p d.sub.p                        (3)

This expression is recognized to give H_(s) as the change of field inpassing from the inside of a particle to the outside of the particle.

Denoting K_(m) as the following constant ##EQU5## then from (2) K_(m)equals the quantity M_(p) /H_(a) -H_(s)) i.e.

    K.sub.m = M.sub.p /(H.sub.a -H.sub.s)                      (5)

Thus, on the graph of M_(p) vs. H_(a) straight lines of slope K_(m)intersecting the measured curve and the H_(a) axis relate correspondingvalues of M_(p) and H_(s). Accordingly a graph may be constructed ofM_(p) vs. H_(s). For example, when the sample is contained in aspherical cavity d_(s) = 1/3, K_(m) is infinite, and H_(s) equals H_(a).For a long sample such that d_(s) = 0, K_(m) is negative and H_(a) isless than H_(s) i.e. the field magnetizing a particle of the sample isgreater than the field applied to the sample.

Additionally, for a process bed, a constant K_(p) may be defined asfollows: ##EQU6##

It may also be seen from Eq. (2) that a line of slope - K_(p) passingthrough a point H_(a) on the horizontal axis of the graph of M_(p) vs.H_(s) intersects the curve on the graph at a value of M_(p) giving theparticle magnetization in the bed. Thus, the particle magnetizationM_(p) in a process bed has been related to the field H_(a) applied tothe process bed.

The relationship of Eq. (1) is an approximation more likely to beaccurate for beds having high voidage than for very densely packedsamples.

It is to be understood that the term "applied magnetic field" usedthroughout the specification and claims refers to an empty vesselapplied magnetic field.

                                      TABLE XXI                                   __________________________________________________________________________               Reaction Conditions                                                Principal Conversion                                                                     Temperature                                                                          Pressure                                                                           Feed Rate                                                                           Hydrogen Rate                                    Desired    ° F.                                                                          psig V/V/Hr.                                                                             scf/Bbl                                          __________________________________________________________________________    Hydrofining                                                                              500-800                                                                               50-2000                                                                           0.1-10.0                                                                            500-10,000                                       Hydrocracking                                                                            450-850                                                                               200-2000                                                                          0.1-10.0                                                                            500-10,000                                       Catalytic Cracking                                                                        700-1000                                                                             0-50                                                                              0.1-20.0                                                                            0                                                Catalytic Reforming                                                                       800-1000                                                                             50-1000                                                                           0.1-20.0                                                                            500-10,000                                       __________________________________________________________________________

It will be understood by those skilled in the art that variousmodifications of the present invention as described in the foregoingexamples may be employed without departing from the scope of theinvention. Many variations and modifications thereof will be apparent tothose skilled in the art and can be made without departing from thespirit and scope of the invention herein described.

What is claimed is:
 1. A fluidized hydrocarbon conversion process whichcomprises:(a) subjecting a fluidized bed comprised of magnetizable,fluidizable composite particles which have catalytic activity forhydrocarbon conversion and which contain 2 to 40 volume % ferro- orferrimagnetic material to a nontime varying and substantially uniformapplied magnetic field having a substantial component along thedirection of gravity such that said composite particles have a componentof magnetization along the direction of gravity, and (b) passing afluidizing gaseous medium comprising a vaporized hydrocarbon feedstockupwardly through said bed at a superficial gas velocity ranging between:(i) at least 10% greater than the normal minimum superficial gasvelocity required to fluidize the bed in the absence of said appliedmagnetic field; and (ii) less than the superficial gas velocity requiredto cause time-varying fluctuations of pressure difference through saidbed for a 0.1 to 1 second time interval during continuous fluidizationin the presence of said applied magnetic field.
 2. The process of claim1 wherein said fluidizing gaseous medium includes hydrogen.
 3. Theprocess of claim 1 wherein said fluidized bed is at a temperature of500-800° F., said fluidizing gaseous medium comprises a vaporizedpetroleum feedstock and hydrogen and said magnetizable, fluidizablecomposite particles are catalytically active for the catalyticdesulfurization of said feedstock.
 4. The process of claim 3 wherein atleast a portion of said bed is subjected to a substantially uniformapplied magnetic field of at least 100 oersteds oriented axially to theflow of gas in the fluidized bed zone and wherein said magnetizable,fluidizable composite particles have a magnetization of at least 150gauss.
 5. The process of claim 1 wherein said fluidized bed is at atemperature of 800-1100° F. and said magnetizable, fluidizable compositeparticles are catalytically active for the catalytic reforming of saidfeedstock.
 6. The process of claim 1 wherein the uppermost 20-40% regionor zone of the bed is stabilized by the applied magnetic field.